Bootstrap v3.2.0 Grid system layout - html

Ok I'm probably missing something really simple here but I can not figure out why my cols are acting like this using twitter bootstrap. This happens when I resize the browser to about 323px. I have no other css styles or html on the page. I have attached 2 screen shots for reference.
I have my columns set accordingly but when I resize the browser to the smallest size it drops the last col-xs-1 down one row.
<div class="container">
<div class="row">
<div class="col-xs-1">1</div>
<div class="col-xs-9">9</div>
<div class="col-xs-1">1</div>
<div class="col-xs-1">1</div>
</div>
</div>
If I was to have 4 col-xs-3 they display correctly horizontally across the browser.
<div class="container">
<div class="row">
<div class="col-xs-3">3</div>
<div class="col-xs-3">3</div>
<div class="col-xs-3">3</div>
<div class="col-xs-3">3</div>
</div>
</div>
Here is the bootply : http://www.bootply.com/xuVoyvjNKr
What am I missing here ?


It's just a question about mathematic...
You have 3 x col-xs-1 and 1 x col-xs-9...
Width of document : 360px....
One col-xs-1 should have a width of : 360/12 = 30px...
But you forgot that the divs col-xx-xx has padding-right and padding-left to 15px...
So : The width of col-xs-1 - padding = 30px - 30px = 0...
You don't have enough place, so it jumps of one line...
It's not the case with col-xs-3 because 360/12*3 = 90px...
If you want you can set the padding to 0 for small views, but the problem will appear again if your screen size is less larger again....

Related

How to flip columns from bootstrap on mobile [duplicate]

I'm making a responsive layout with a top fixed navbar. Underneath I have two columns, one for a sidebar (3), and one for content (9). Which on desktop looks like this
navbar
[3][9]
When I resize to mobile the navbar is compressed and hidden, then the sidebar is stacked on top of the content, like this:
navbar
[3]
[9]
I would like the main content at the top, so I need to change the order on mobile to this:
navbar
[9]
[3]
I found this article which covers the same points, but the accepted answer has been edited to say that the solution no applies to the current version of Bootstrap.
How can I reorder these columns on mobile? Or alternatively, how can I get the sidbar list-group into my expanding navbar?
Here is my code:
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<!-- Latest compiled and minified CSS -->
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css" integrity="sha384-BVYiiSIFeK1dGmJRAkycuHAHRg32OmUcww7on3RYdg4Va+PmSTsz/K68vbdEjh4u" crossorigin="anonymous">
<!-- Optional theme -->
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap-theme.min.css" integrity="sha384-rHyoN1iRsVXV4nD0JutlnGaslCJuC7uwjduW9SVrLvRYooPp2bWYgmgJQIXwl/Sp" crossorigin="anonymous">
<!-- Latest compiled and minified JavaScript -->
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js" integrity="sha384-Tc5IQib027qvyjSMfHjOMaLkfuWVxZxUPnCJA7l2mCWNIpG9mGCD8wGNIcPD7Txa" crossorigin="anonymous"></script>
<div class="navbar navbar-inverse navbar-static-top">
<div class="container">
Brand Title
<button class="navbar-toggle" data-toggle="collapse" data-target=".navHeaderCollapse">
<span class="icon-bar"></span>
<span class="icon-bar"></span>
<span class="icon-bar"></span>
</button>
<div class="collapse navbar-collapse navHeaderCollapse">
<ul class="nav navbar-nav navbar-right"><!--original navbar-->
<li class="active">Home</li>
<li>FAQ</li>
</ul>
</div>
</div>
</div><!--End Navbar Div-->
<div class="container">
<div class="row">
<div class="col-lg-3">
<div class="list-group">
<a href="#" class="list-group-item">
<h4 class="list-group-item-heading">Lorem ipsum</h4>
<p class="list-group-item-text">Lorem Ipsum is simply dummy text.</p></a>
</div>
</div><!--end sidebar-->
<div class="col-lg-9">
<div class="panel panel-default">
<div class="panel-body">
<div class="page-header">
Main Content
</div>
</div>
</div><!--end main content area-->

You cannot change the order of columns in smaller screens but you can do that in large screens.
So change the order of your columns.
<!--Main Content-->
<div class="col-lg-9 col-lg-push-3">
</div>
<!--Sidebar-->
<div class="col-lg-3 col-lg-pull-9">
</div>
By default this displays the main content first.
So in mobile main content is displayed first.
By using col-lg-push and col-lg-pull we can reorder the columns in large screens and display sidebar on the left and main content on the right.
Working fiddle here.

Updated 2018
For the original question based on Bootstrap 3, the solution was to use push-pull.
In Bootstrap 4 it's now possible to change the order, even when the columns are full-width stacked vertically, thanks to Bootstrap 4 flexbox. OFC, the push pull method will still work, but now there are other ways to change column order in Bootstrap 4, making it possible to re-order full-width columns.
Method 1 - Use flex-column-reverse for xs screens:
<div class="row flex-column-reverse flex-md-row">
<div class="col-md-3">
sidebar
</div>
<div class="col-md-9">
main
</div>
</div>
Method 2 - Use order-first for xs screens:
<div class="row">
<div class="col-md-3">
sidebar
</div>
<div class="col-md-9 order-first order-md-last">
main
</div>
</div>
Bootstrap 4(alpha 6): http://www.codeply.com/go/bBMOsvtJhD
Bootstrap 4.1: https://www.codeply.com/go/e0v77yGtcr
Original 3.x Answer
For the original question based on Bootstrap 3, the solution was to use push-pull for the larger widths, and then the columns will show is their natural order on smaller (xs) widths. (A-B reverse to B-A).
<div class="container">
<div class="row">
<div class="col-md-9 col-md-push-3">
main
</div>
<div class="col-md-3 col-md-pull-9">
sidebar
</div>
</div>
</div>
Bootstrap 3: http://www.codeply.com/go/wgzJXs3gel
#emre stated, "You cannot change the order of columns in smaller screens but you can do that in large screens". However, this should be clarified to state: "You cannot change the order of full-width "stacked" columns.." in Bootstrap 3.

Bootstrap 3 Answer
The answers here work for just 2 cells, but as soon as those columns have more in them it can lead to a bit more complexity. I think I've found a generalized solution for any number of cells in multiple columns.
Goals
Get a vertical sequence of tags on mobile to arrange themselves in whatever order the design calls for on tablet/desktop. In this concrete example, one tag must enter flow earlier than it normally would, and another later than it normally would.
Mobile
[1 headline]
[2 image]
[3 qty]
[4 caption]
[5 desc]
Tablet+
[2 image ][1 headline]
[ ][3 qty ]
[ ][5 desc ]
[4 caption][ ]
[ ][ ]
So headline needs to shuffle right on tablet+, and technically, so does desc - it sits above the caption tag that precedes it on mobile. You'll see in a moment 4 caption is in trouble too.
Let's assume every cell could vary in height, and needs to be flush top-to-bottom with its next cell (ruling out weak tricks like a table).
As with all Bootstrap Grid problems step 1 is to realize the HTML has to be in mobile-order, 1 2 3 4 5, on the page. Then, determine how to get tablet/desktop to reorder itself in this way - ideally without Javascript.
The solution to get 1 headline and 3 qty to sit to the right not the left is to simply set them both pull-right. This applies CSS float: right, meaning they find the first open space they'll fit to the right. You can think of the browser's CSS processor working in the following order: 1 fits in to the right top corner. 2 is next and is regular (float: left), so it goes to top-left corner. Then 3, which is float: right so it leaps over underneath 1.
But this solution wasn't enough for 4 caption; because the right 2 cells are so short 2 image on the left tends to be longer than the both of them combined. Bootstrap Grid is a glorified float hack, meaning 4 caption is float: left. With 2 image occupying so much room on the left, 4 caption attempts to fit in the next available space - often the right column, not the left where we wanted it.
The solution here (and more generally for any issue like this) was to add a hack tag, hidden on mobile, that exists on tablet+ to push caption out, that then gets covered up by a negative margin - like this:
[2 image ][1 headline]
[ ][3 qty ]
[ ][4 hack ]
[5 caption][6 desc ^^^]
[ ][ ]
http://jsfiddle.net/b9chris/52VtD/16633/
HTML:
<div id=headline class="col-xs-12 col-sm-6 pull-right">Product Headline</div>
<div id=image class="col-xs-12 col-sm-6">Product Image</div>
<div id=qty class="col-xs-12 col-sm-6 pull-right">Qty, Add to cart</div>
<div id=hack class="hidden-xs col-sm-6">Hack</div>
<div id=caption class="col-xs-12 col-sm-6">Product image caption</div>
<div id=desc class="col-xs-12 col-sm-6 pull-right">Product description</div>
CSS:
#hack { height: 50px; }
#media (min-width: #screen-sm) {
#desc { margin-top: -50px; }
}
So, the generalized solution here is to add hack tags that can disappear on mobile. On tablet+ the hack tags allow displayed tags to appear earlier or later in the flow, then get pulled up or down to cover up those hack tags.
Note: I've used fixed heights for the sake of the simple example in the linked jsfiddle, but the actual site content I was working on varies in height in all 5 tags. It renders properly with relatively large variance in tag heights, especially image and desc.
Note 2: Depending on your layout, you may have a consistent enough column order on tablet+ (or larger resolutions), that you can avoid use of hack tags, using margin-bottom instead, like so:
Note 3: This uses Bootstrap 3. Bootstrap 4 uses a different grid set, and won't work with these examples.
http://jsfiddle.net/b9chris/52VtD/16632/

October 2017
I would like to add another Bootstrap 4 solution. One that worked for me.
The CSS "Order" property, combined with a media query, can be used to re-order columns when they get stacked in smaller screens.
Something like this:
#media only screen and (max-width: 768px) {
#first {
order: 2;
}
#second {
order: 4;
}
#third {
order: 1;
}
#fourth {
order: 3;
}
}
CodePen Link: https://codepen.io/preston206/pen/EwrXqm
Adjust the screen size and you'll see the columns get stacked in a different order.
I'll tie this in with the original poster's question. With CSS, the navbar, sidebar, and content can be targeted and then order properties applied within a media query.

In Bootstrap 4, if you want to do something like this:
Mobile | Desktop
-----------------------------
A | A
C | B C
B | D
D |
You need to reverse the order of B then C then apply order-{breakpoint}-first to B. And apply two different settings, one that will make them share the same cols and other that will make them take the full width of the 12 cols:
Smaller screens: 12 cols to B and 12 cols to C
Larger screens: 12 cols between the sum of them (B + C = 12)
Like this
<div class='row no-gutters'>
<div class='col-12'>
A
</div>
<div class='col-12'>
<div class='row no-gutters'>
<div class='col-12 col-md-6'>
C
</div>
<div class='col-12 col-md-6 order-md-first'>
B
</div>
</div>
</div>
<div class='col-12'>
D
</div>
</div>
Demo: https://codepen.io/anon/pen/wXLGKa

Starting with the mobile version first, you can achieve what you want, most of the time.
Examples here:
http://jsbin.com/wulexiq/edit?html,css,output
<div class="container">
<h1>PUSH - PULL Bootstrap demo</h1>
<h2>Version 1:</h2>
<div class="row">
<div class="col-xs-12 col-sm-5 col-sm-push-3 green">
IN MIDDLE ON SMALL/MEDIUM/LARGE SCREEN
<hr> TOP ROW XS-SMALL SCREEN
</div>
<div class="col-xs-12 col-sm-4 col-sm-push-3 gold">
TO THE RIGHT ON SMALL/MEDIUM/LARGE SCREEN
<hr> MIDDLE ROW ON XS-SMALL
</div>
<div class="col-xs-12 col-sm-3 col-sm-pull-9 red">
TO THE LEFT ON SMALL/MEDIUM/LARGE SCREEN
<hr> BOTTOM ROW ON XS-SMALL
</div>
</div>
<h2>Version 2:</h2>
<div class="row">
<div class="col-xs-12 col-sm-4 col-sm-push-8 yellow">
TO THE RIGHT ON SMALL/MEDIUM/LARGE SCREEN
<hr> TOP ROW ON XS-SMALL
</div>
<div class="col-xs-12 col-sm-4 col-sm-pull-4 blue">
TO THE LEFT ON SMALL/MEDIUM/LARGE SCREEN
<hr> MIDDLE ROW XS-SMALL SCREEN
</div>
<div class="col-xs-12 col-sm-4 col-sm-pull-4 pink">
IN MIDDLE ON SMALL/MEDIUM/LARGE SCREEN
<hr> BOTTOM ROW ON XS-SMALL
</div>
</div>
<h2>Version 3:</h2>
<div class="row">
<div class="col-xs-12 col-sm-5 cyan">
TO THE LEFT ON SMALL/MEDIUM/LARGE SCREEN TOP ROW ON XS-SMALL
</div>
<div class="col-xs-12 col-sm-3 col-sm-push-4 orange">
TO THE RIGHT ON SMALL/MEDIUM/LARGE SCREEN
<hr> MIDDLE ROW ON XS-SMALL
</div>
<div class="col-xs-12 col-sm-4 col-sm-pull-3 brown">
IN THE MIDDLE ON SMALL/MEDIUM/LARGE SCREEN
<hr> BOTTOM ROW XS-SMALL SCREEN
</div>
</div>
<h2>Version 4:</h2>
<div class="row">
<div class="col-xs-12 col-sm-4 col-sm-push-8 darkblue">
TO THE RIGHT ON SMALL/MEDIUM/LARGE SCREEN
<hr> TOP ROW XS-SMALL SCREEN
</div>
<div class="col-xs-12 col-sm-4 beige">
MIDDLE ON SMALL/MEDIUM/LARGE SCREEN
<hr> MIDDLE ROW ON XS-SMALL
</div>
<div class="col-xs-12 col-sm-4 col-sm-pull-8 silver">
TO THE LEFT ON SMALL/MEDIUM/LARGE SCREEN
<hr> BOTTOM ROW ON XS-SMALL
</div>
</div>
</div>

This is quite easy with jQuery using insertAfter() or insertBefore():
<div class="left">content</div>
<div class="right">sidebar</div>
<script>
$('.right').insertBefore('left');
</script>
If you want to to set o condition for mobile devices you can make it like this:
<script>
var $iW = $(window).innerWidth();
if ($iW < 992){
$('.right').insertBefore('.left');
}else{
$('.right').insertAfter('.left');
}
</script>
example
https://jsfiddle.net/w9n27k23/

Its very simple, write your html the way you would want it to be viewed in mobile. Then using the bootstrap order class you can arrange how you want it to viewed on desktop.
<html>
<head>
<title>Order View</title>
<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/bootstrap#5.1.3/dist/css/bootstrap.min.css" integrity="sha384-1BmE4kWBq78iYhFldvKuhfTAU6auU8tT94WrHftjDbrCEXSU1oBoqyl2QvZ6jIW3" crossorigin="anonymous">
</head>
<body>
<div class="row">
<div class="col order-md-2">
<h1>IMAGE</h1>
</div>
<div class="col order-md-1">
<h1>TEXT</h1>
</div>
</body>
</html>

What column system to use in Responsive Design in BootStrap

I am a complete beginner and I am learning Bootstrap. I want to know how to determine which column system I need to use in my website. Suppose I have a row with 3 columns. Now I have 3 options.
Option 1:
<div class="row">
<div class="col-md-4">
</div>
<div class="col-md-4">
</div>
<div class="col-md-4">
</div>
</div>
Option 2:
<div class="row">
<div class="col-lg-4">
</div>
<div class="col-lg-4">
</div>
<div class="col-lg-4">
</div>
</div>
Option 3:
<div class="row">
<div class="col-sm-4">
</div>
<div class="col-sm-4">
</div>
<div class="col-sm-4">
</div>
</div>
Now my question is, As I want my website to be responsive which class I need to apply. I want my website to render properly irrespective of device selected. I understood that they are meant for different devices. Does that mean, I need to write 3 different css style code (I doubt it). So, what shall I put in my code?
P.S: I saw this link SO LINK and I understood it. But still I am confused, what to put in my code? Shall I put sm,lg or md?

These define the width of the screen at which the layout will collapse. For example, in .col-md-, the layout will be horizontal until the screen width is less than 970px, at this point, the layout will collapse. However, if you use .col-lg-, the layout will be horizontal until the screen width is less than 1170px, then it will collapse.
Bootstrap has 4 breakpoints, .col-xs-, .col-sm-, .col-md- and .col-lg-. You should use these depending on the content of the div. The best way to become familiar is to play around with each one and notice that the layout collapses at different points for each one when you decrease the width of your window. So to answer the question, you should choose whichever one collapses correctly for the content of your div. Hope this helps.
For a more detailed guide on the bootstrap grid system, take at look at this: https://www.w3schools.com/bootstrap/bootstrap_grid_system.asp
I found it helpful to get a good understanding.

I generally use col-md prefix, so I guess your first option would work quite fine: col-md-4.

To add to the other suggestions you've received, remember that you can apply multiple Bootstrap column classes to the same div.
For example say you wanted 3 equal width columns on a wide viewport. Then as the viewport narrows this changes to one full width header with two equal width columns below, and on smartphones all three divs are stacked vertically, then you might use something like
<div class="container">
<div class="row">
<div class="col-lg-4 col-md-12">column1
</div>
<div class="col-lg-4 col-md-6">colmun2
</div>
<div class="col-lg-4 col-md-6">column3
</div>
</div>
</div>
See this live https://codepen.io/panchroma/pen/EwVwpw
Or you might want to change the relative widths of your 3 columns at different viewports
<div class="row">
<div class="col-lg-6 col-md-4">
</div>
<div class="col-lg-3 col-md-4">
</div>
<div class="col-lg-3 col-md-4">
</div>
</div>
Or you might want to hide one of the columns at narrower viewports
<div class="row">
<div class="col-md-4">
</div>
<div class="col-md-4">
</div>
<div class="col-md-4 hidden-sm hidden-xs">
</div>
</div>
The important thing is that you can mix and match your classes to achieve the responsive behaviour that you need.
Once you get the hang of the grid sizing options you might also want to check out how to reorder columns. What often happens is that you need to have a different column order on desktop and mobile, and there will probably be times when you want to offset columns as well.
Good luck!

How to set margin/padding for a device

Im making my website responsive for devices but i want to know if i can set a grid or margin/padding property for iphone so i can place it nicely and not 2 paragraphs in eachother.
I already tried to grid some text but it still looks weird in eachother this is my code:
<div class="row">
<div class="col-xs-1 col-lg-12">
Thisismy Test
</div>
</div>

You haven't tagged this as being a Bootstrap grid, but I'm assuming it is because of your grid classes.
You mention that you want to stop the navbar-brand text from wrapping on an iPhone so I'm wondering if there's there a reason why you wouldn't make the navbar-brand parent wider?
It looks to me as if it would need to be minimum col-xs-5
Here's a example showing both your existing HTML and the modification
https://codepen.io/panchroma/pen/OgQxBw
HTML
<div class="row">
<div class="col-xs-5 col-lg-12">
Thisismy Test
</div>
</div>

If you want to show the paragraph in entire row in mobile , use col-xs-12 class which will occupy the entire row space and display everything in one row in all th escreen sizes.
<div class="row">
<div class="col-xs-12">
Thisismy Test
</div>
</div>
If you want to display 2 paragraphs in row side by side use col-xs-6 for each div
<div class="row">
<div class="col-xs-6 col-lg-12">
Thisismy Test
</div>
<div class="col-xs-6 col-lg-12">
Thisismy Test
</div>
</div>
If you want to write your own CSS , you can do that by using media queries to define custom CSS for different screen sizes https://developer.mozilla.org/en-US/docs/Web/CSS/Media_Queries/Using_media_queries

Bootstrap Column Reordering Sizing Problems

I'm trying to reorder the columns on my website via Bootstrap's method of reordering columns depending on the screen size which works fine for most of the responsive layouts I'm testing apart from 1.
The layout having problems is the Tablet Landscape Layout (1024 x 768) which displays like this:
Every other screen displays the blue div and the right div either with the red div on top if the screen is too small or on the right with the blue div aligning itself exactly next to it if the screen is large enough.
This is the code I'm using right now:
<div class="container">
<div class="col-xs-12 col-sm-12 col-md-12 col-lg-12 col-xl-12">
<div class="row clearfix">
<div class="col-xs-12 col-sm-12 col-md-push-8 col-md-4 col-lg-push-8 col-lg-4 col-xl-push-8 col-xl-4" style="background: red">
Basket
</div>
<div class="col-xs-12 col-sm-12 col-md-pull-8 col-md-8 col-lg-pull-4 col-lg-8 col-xl-pull-8 col-xl-8" style="background: blue">
News
</div>
</div>
</div>
</div>
Does anyone know why the blue div is so far to the right on the Tablet Landscape layout rather than touching the red div like it should?

Some general markup issues:
First of all, there's no col-xl-*, so you can get rid of those.
Secondly, you don't need col-xs-12, since the default is for it take up the whole width unless otherwise specified.
Third, Bootstrap is mobile first, so larger sizes will override the existing smaller sizes, meaning if you don't intend on changing something, there's no need to specify the larger size again.
The actual issue is that col-*-pull-* is relative to where the element would be placed. Bear in mind, you haven't changed anything in the document flow. So the elements are positioned normally and then phase shifted with left or right. Since the blue container would normally start 4 columns over, you only need to pull it back by 4 columns, instead of 8.
The whole thing can be rewritten like this:
.red { background: red }
.blue { background: blue }
<link href="//cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/3.3.2/css/bootstrap.css" rel="stylesheet"/>
<div class="container">
<div class="row ">
<div class="col-md-4 col-md-push-8 red"> Basket </div>
<div class="col-md-8 col-md-pull-4 blue"> News </div>
</div>
</div>

How do I change Bootstrap 3 column order on mobile layout?

I'm making a responsive layout with a top fixed navbar. Underneath I have two columns, one for a sidebar (3), and one for content (9). Which on desktop looks like this
navbar
[3][9]
When I resize to mobile the navbar is compressed and hidden, then the sidebar is stacked on top of the content, like this:
navbar
[3]
[9]
I would like the main content at the top, so I need to change the order on mobile to this:
navbar
[9]
[3]
I found this article which covers the same points, but the accepted answer has been edited to say that the solution no applies to the current version of Bootstrap.
How can I reorder these columns on mobile? Or alternatively, how can I get the sidbar list-group into my expanding navbar?
Here is my code:
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<!-- Latest compiled and minified CSS -->
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css" integrity="sha384-BVYiiSIFeK1dGmJRAkycuHAHRg32OmUcww7on3RYdg4Va+PmSTsz/K68vbdEjh4u" crossorigin="anonymous">
<!-- Optional theme -->
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap-theme.min.css" integrity="sha384-rHyoN1iRsVXV4nD0JutlnGaslCJuC7uwjduW9SVrLvRYooPp2bWYgmgJQIXwl/Sp" crossorigin="anonymous">
<!-- Latest compiled and minified JavaScript -->
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js" integrity="sha384-Tc5IQib027qvyjSMfHjOMaLkfuWVxZxUPnCJA7l2mCWNIpG9mGCD8wGNIcPD7Txa" crossorigin="anonymous"></script>
<div class="navbar navbar-inverse navbar-static-top">
<div class="container">
Brand Title
<button class="navbar-toggle" data-toggle="collapse" data-target=".navHeaderCollapse">
<span class="icon-bar"></span>
<span class="icon-bar"></span>
<span class="icon-bar"></span>
</button>
<div class="collapse navbar-collapse navHeaderCollapse">
<ul class="nav navbar-nav navbar-right"><!--original navbar-->
<li class="active">Home</li>
<li>FAQ</li>
</ul>
</div>
</div>
</div><!--End Navbar Div-->
<div class="container">
<div class="row">
<div class="col-lg-3">
<div class="list-group">
<a href="#" class="list-group-item">
<h4 class="list-group-item-heading">Lorem ipsum</h4>
<p class="list-group-item-text">Lorem Ipsum is simply dummy text.</p></a>
</div>
</div><!--end sidebar-->
<div class="col-lg-9">
<div class="panel panel-default">
<div class="panel-body">
<div class="page-header">
Main Content
</div>
</div>
</div><!--end main content area-->

You cannot change the order of columns in smaller screens but you can do that in large screens.
So change the order of your columns.
<!--Main Content-->
<div class="col-lg-9 col-lg-push-3">
</div>
<!--Sidebar-->
<div class="col-lg-3 col-lg-pull-9">
</div>
By default this displays the main content first.
So in mobile main content is displayed first.
By using col-lg-push and col-lg-pull we can reorder the columns in large screens and display sidebar on the left and main content on the right.
Working fiddle here.

Updated 2018
For the original question based on Bootstrap 3, the solution was to use push-pull.
In Bootstrap 4 it's now possible to change the order, even when the columns are full-width stacked vertically, thanks to Bootstrap 4 flexbox. OFC, the push pull method will still work, but now there are other ways to change column order in Bootstrap 4, making it possible to re-order full-width columns.
Method 1 - Use flex-column-reverse for xs screens:
<div class="row flex-column-reverse flex-md-row">
<div class="col-md-3">
sidebar
</div>
<div class="col-md-9">
main
</div>
</div>
Method 2 - Use order-first for xs screens:
<div class="row">
<div class="col-md-3">
sidebar
</div>
<div class="col-md-9 order-first order-md-last">
main
</div>
</div>
Bootstrap 4(alpha 6): http://www.codeply.com/go/bBMOsvtJhD
Bootstrap 4.1: https://www.codeply.com/go/e0v77yGtcr
Original 3.x Answer
For the original question based on Bootstrap 3, the solution was to use push-pull for the larger widths, and then the columns will show is their natural order on smaller (xs) widths. (A-B reverse to B-A).
<div class="container">
<div class="row">
<div class="col-md-9 col-md-push-3">
main
</div>
<div class="col-md-3 col-md-pull-9">
sidebar
</div>
</div>
</div>
Bootstrap 3: http://www.codeply.com/go/wgzJXs3gel
#emre stated, "You cannot change the order of columns in smaller screens but you can do that in large screens". However, this should be clarified to state: "You cannot change the order of full-width "stacked" columns.." in Bootstrap 3.

Bootstrap 3 Answer
The answers here work for just 2 cells, but as soon as those columns have more in them it can lead to a bit more complexity. I think I've found a generalized solution for any number of cells in multiple columns.
Goals
Get a vertical sequence of tags on mobile to arrange themselves in whatever order the design calls for on tablet/desktop. In this concrete example, one tag must enter flow earlier than it normally would, and another later than it normally would.
Mobile
[1 headline]
[2 image]
[3 qty]
[4 caption]
[5 desc]
Tablet+
[2 image ][1 headline]
[ ][3 qty ]
[ ][5 desc ]
[4 caption][ ]
[ ][ ]
So headline needs to shuffle right on tablet+, and technically, so does desc - it sits above the caption tag that precedes it on mobile. You'll see in a moment 4 caption is in trouble too.
Let's assume every cell could vary in height, and needs to be flush top-to-bottom with its next cell (ruling out weak tricks like a table).
As with all Bootstrap Grid problems step 1 is to realize the HTML has to be in mobile-order, 1 2 3 4 5, on the page. Then, determine how to get tablet/desktop to reorder itself in this way - ideally without Javascript.
The solution to get 1 headline and 3 qty to sit to the right not the left is to simply set them both pull-right. This applies CSS float: right, meaning they find the first open space they'll fit to the right. You can think of the browser's CSS processor working in the following order: 1 fits in to the right top corner. 2 is next and is regular (float: left), so it goes to top-left corner. Then 3, which is float: right so it leaps over underneath 1.
But this solution wasn't enough for 4 caption; because the right 2 cells are so short 2 image on the left tends to be longer than the both of them combined. Bootstrap Grid is a glorified float hack, meaning 4 caption is float: left. With 2 image occupying so much room on the left, 4 caption attempts to fit in the next available space - often the right column, not the left where we wanted it.
The solution here (and more generally for any issue like this) was to add a hack tag, hidden on mobile, that exists on tablet+ to push caption out, that then gets covered up by a negative margin - like this:
[2 image ][1 headline]
[ ][3 qty ]
[ ][4 hack ]
[5 caption][6 desc ^^^]
[ ][ ]
http://jsfiddle.net/b9chris/52VtD/16633/
HTML:
<div id=headline class="col-xs-12 col-sm-6 pull-right">Product Headline</div>
<div id=image class="col-xs-12 col-sm-6">Product Image</div>
<div id=qty class="col-xs-12 col-sm-6 pull-right">Qty, Add to cart</div>
<div id=hack class="hidden-xs col-sm-6">Hack</div>
<div id=caption class="col-xs-12 col-sm-6">Product image caption</div>
<div id=desc class="col-xs-12 col-sm-6 pull-right">Product description</div>
CSS:
#hack { height: 50px; }
#media (min-width: #screen-sm) {
#desc { margin-top: -50px; }
}
So, the generalized solution here is to add hack tags that can disappear on mobile. On tablet+ the hack tags allow displayed tags to appear earlier or later in the flow, then get pulled up or down to cover up those hack tags.
Note: I've used fixed heights for the sake of the simple example in the linked jsfiddle, but the actual site content I was working on varies in height in all 5 tags. It renders properly with relatively large variance in tag heights, especially image and desc.
Note 2: Depending on your layout, you may have a consistent enough column order on tablet+ (or larger resolutions), that you can avoid use of hack tags, using margin-bottom instead, like so:
Note 3: This uses Bootstrap 3. Bootstrap 4 uses a different grid set, and won't work with these examples.
http://jsfiddle.net/b9chris/52VtD/16632/

October 2017
I would like to add another Bootstrap 4 solution. One that worked for me.
The CSS "Order" property, combined with a media query, can be used to re-order columns when they get stacked in smaller screens.
Something like this:
#media only screen and (max-width: 768px) {
#first {
order: 2;
}
#second {
order: 4;
}
#third {
order: 1;
}
#fourth {
order: 3;
}
}
CodePen Link: https://codepen.io/preston206/pen/EwrXqm
Adjust the screen size and you'll see the columns get stacked in a different order.
I'll tie this in with the original poster's question. With CSS, the navbar, sidebar, and content can be targeted and then order properties applied within a media query.

In Bootstrap 4, if you want to do something like this:
Mobile | Desktop
-----------------------------
A | A
C | B C
B | D
D |
You need to reverse the order of B then C then apply order-{breakpoint}-first to B. And apply two different settings, one that will make them share the same cols and other that will make them take the full width of the 12 cols:
Smaller screens: 12 cols to B and 12 cols to C
Larger screens: 12 cols between the sum of them (B + C = 12)
Like this
<div class='row no-gutters'>
<div class='col-12'>
A
</div>
<div class='col-12'>
<div class='row no-gutters'>
<div class='col-12 col-md-6'>
C
</div>
<div class='col-12 col-md-6 order-md-first'>
B
</div>
</div>
</div>
<div class='col-12'>
D
</div>
</div>
Demo: https://codepen.io/anon/pen/wXLGKa

Starting with the mobile version first, you can achieve what you want, most of the time.
Examples here:
http://jsbin.com/wulexiq/edit?html,css,output
<div class="container">
<h1>PUSH - PULL Bootstrap demo</h1>
<h2>Version 1:</h2>
<div class="row">
<div class="col-xs-12 col-sm-5 col-sm-push-3 green">
IN MIDDLE ON SMALL/MEDIUM/LARGE SCREEN
<hr> TOP ROW XS-SMALL SCREEN
</div>
<div class="col-xs-12 col-sm-4 col-sm-push-3 gold">
TO THE RIGHT ON SMALL/MEDIUM/LARGE SCREEN
<hr> MIDDLE ROW ON XS-SMALL
</div>
<div class="col-xs-12 col-sm-3 col-sm-pull-9 red">
TO THE LEFT ON SMALL/MEDIUM/LARGE SCREEN
<hr> BOTTOM ROW ON XS-SMALL
</div>
</div>
<h2>Version 2:</h2>
<div class="row">
<div class="col-xs-12 col-sm-4 col-sm-push-8 yellow">
TO THE RIGHT ON SMALL/MEDIUM/LARGE SCREEN
<hr> TOP ROW ON XS-SMALL
</div>
<div class="col-xs-12 col-sm-4 col-sm-pull-4 blue">
TO THE LEFT ON SMALL/MEDIUM/LARGE SCREEN
<hr> MIDDLE ROW XS-SMALL SCREEN
</div>
<div class="col-xs-12 col-sm-4 col-sm-pull-4 pink">
IN MIDDLE ON SMALL/MEDIUM/LARGE SCREEN
<hr> BOTTOM ROW ON XS-SMALL
</div>
</div>
<h2>Version 3:</h2>
<div class="row">
<div class="col-xs-12 col-sm-5 cyan">
TO THE LEFT ON SMALL/MEDIUM/LARGE SCREEN TOP ROW ON XS-SMALL
</div>
<div class="col-xs-12 col-sm-3 col-sm-push-4 orange">
TO THE RIGHT ON SMALL/MEDIUM/LARGE SCREEN
<hr> MIDDLE ROW ON XS-SMALL
</div>
<div class="col-xs-12 col-sm-4 col-sm-pull-3 brown">
IN THE MIDDLE ON SMALL/MEDIUM/LARGE SCREEN
<hr> BOTTOM ROW XS-SMALL SCREEN
</div>
</div>
<h2>Version 4:</h2>
<div class="row">
<div class="col-xs-12 col-sm-4 col-sm-push-8 darkblue">
TO THE RIGHT ON SMALL/MEDIUM/LARGE SCREEN
<hr> TOP ROW XS-SMALL SCREEN
</div>
<div class="col-xs-12 col-sm-4 beige">
MIDDLE ON SMALL/MEDIUM/LARGE SCREEN
<hr> MIDDLE ROW ON XS-SMALL
</div>
<div class="col-xs-12 col-sm-4 col-sm-pull-8 silver">
TO THE LEFT ON SMALL/MEDIUM/LARGE SCREEN
<hr> BOTTOM ROW ON XS-SMALL
</div>
</div>
</div>

This is quite easy with jQuery using insertAfter() or insertBefore():
<div class="left">content</div>
<div class="right">sidebar</div>
<script>
$('.right').insertBefore('left');
</script>
If you want to to set o condition for mobile devices you can make it like this:
<script>
var $iW = $(window).innerWidth();
if ($iW < 992){
$('.right').insertBefore('.left');
}else{
$('.right').insertAfter('.left');
}
</script>
example
https://jsfiddle.net/w9n27k23/

Its very simple, write your html the way you would want it to be viewed in mobile. Then using the bootstrap order class you can arrange how you want it to viewed on desktop.
<html>
<head>
<title>Order View</title>
<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/bootstrap#5.1.3/dist/css/bootstrap.min.css" integrity="sha384-1BmE4kWBq78iYhFldvKuhfTAU6auU8tT94WrHftjDbrCEXSU1oBoqyl2QvZ6jIW3" crossorigin="anonymous">
</head>
<body>
<div class="row">
<div class="col order-md-2">
<h1>IMAGE</h1>
</div>
<div class="col order-md-1">
<h1>TEXT</h1>
</div>
</body>
</html>