w3.org/TR/CSS2 says:
For other elements, if the element's position is 'relative' or 'static', the containing block is formed by the content edge of the nearest block container ancestor box.
What does it mean? I read it as position: relative doesn't affect an element itself, but actually affects its parent - the containing block.
So, to change CSS of the containing block do I have to apply position to its child?
Isn't it strange? There is a pattern when you apply position: relative to a parent, and position: absolute to some of its child to make that absolutely positioned child be tied to a parent.
...actually affects its parent - the containing block.
The point of
... if the element's position is 'relative' or 'static', the containing
block is formed by the content edge of the nearest block container
ancestor box.
is to explain that its parent is not necessarily its containing block.
Most notably, if it is position:relative and its parent is display:inline, then its parent is not its containing block, but an element further up the DOM tree is instead.
position: relative means that the element which has been given a relative position will adjust itself relative to itself. For example:
An h1 is given the following CSS:
h1 {
position: relative;
top: 20px;
left: 20px;
}
then it will move 20px top and left from its original position. Check my fiddle: https://jsfiddle.net/w6sowku5/
Related
I am a little confused about absolute positioning right now. I have always thought that if I position an element absolutely it would be positioned relative to it's parent element (in contrast to relative to it's usual position like relative positioning). During homework I now came across this situation and I'm confused:
<body>
<div> <!-- This is colored red in my example -->
...
</div>
<div style="position: absolute;"> <!-- This is colored green in my example -->
...
</div>
</body>
What I would expect:
What I got:
Of course when I set an actual position with left/right/top/bottom I get what I would expect from an absolutely positioned element. So is position: absolute just set to take the exact position it would be at without position: absolute when not specified otherwise?
To clarify:
"I have always thought that if I position an element absolutely it would
be positioned relative to it's parent element"
Nope. If an element has position: absolute;, it is positioned relative to the nearest parent in the DOM chain that has position: relative; or position: absolute; specified on it. If no parents have it (ie. they are all position: static, which is the default), then it is positioned relative to the document (page).
When using position: absolute, always:
Be aware of what parent you want it positioned relative to, and make sure that parent has position: relative; on it.
Specify one or more of the top/right/bottom/left attributes on the absolutely positioned object.
You are confused with the difference between position and display.
Position will change which element your element will be positioned relative to. In your case, your child div is now positioned to the body element. That's why it's on top.
Also you need to be aware that div is displayed as block, which means it will take all the width. If you want to align 2 divs left and right, the modern way is to use flexbox. The old way is float left/right.
I have made an article to explain CSS position in details:
https://www.youtube.com/watch?v=nGN5CohGVTI
In css2.1 spec, it says:
A floated box is shifted to the left or right until its outer edge touches the containing block edge or the outer edge of another float.
I wonder what's the containing block of floated elements, and I test:
body {
position: relative;
margin: 5px;
padding: 10px;
}
p {
float: left;
position: absolute;
margin: 10px;
}
<body>
<p>hehe</p>
</body>
According to css2.1 spec, the absolute positioned element's containing block is the nearest positioned block container's padding box.
But in the code above, the floated element is floated to the content box boundary. I'm confused how to find the containing block of the floated element.
The premise of your question is flawed. An absolutely positioned element cannot float, and a float cannot be absolutely positioned. From section 9.7:
[...] if 'position' has the value 'absolute' or 'fixed', the box is absolutely positioned, the computed value of 'float' is 'none' [...]
So you're not trying to find the containing block of a float here. You're trying to find the containing block of an absposed element.
Having said that, if you really must know, the containing block of a float is the same as for relatively positioned or non-positioned elements as I described in my answer to your previous question, since floats cannot be absposed.
I have two elements: one with relative positioning that defines most of my header, and a smaller one that I'd like to "float" on top of it.
<div id=floater style="float:right">
Floater!
</div>
<div id=header style="width: 100%; position: relative; background-color: lightgreen">
This is the header
</div>
As shown in this fiddle, the floated component is invisible. But if you remove the position: relative, the floated element pops right up. Futzing with the z-index hasn't yielded anything of interest.
The header component isn't "mine"; it's inherited through React-Bootstrap. I could override, but right now I'm mostly looking to understand the interaction of float and relative positioning.
Elements without a position property set will default to "position:static" which ignores all positioning properties such as z-index. By setting relative positioning to the header element you have introduced the z-index positioning property to that element bringing it in front of the floater element which does not have a z-index property.
Since z-index will be ignored with a static floater element you will have to give that element a position property (absolute, relative or fixed) so it can have z-index as well.
For your example "position: relative;" would work. Once you have set the position property on the floater element you would need to add a z-index value to it that's higher then the header element. Which in this case z-index:1 would be a higher value since z-index is set to default.
Example:
<div id=floater style="float:right; position: relative; z-index: 1;">
Floater!
</div>
<div id=header style="width: 100%; position: relative; background-color: lightgreen">
This is the header
</div>
When elements are positioned, they can overlap other elements. If two positioned elements overlap without a z-index specified, the element positioned last in the HTML code will be shown on top.
This is a function of the painting order
In-flow, non-positioned, block-level elements are painted in step 4
Floated items are painted at step 5. So the floated element is painted "on top" of the static div and you see it displayed.
But positioned descendants with 'z-index: auto' or 'z-index: 0' are painted in step 8. So adding position:relative to the div means that it is now painted "on top" of the floated element, hiding it.
Please bear with me... and excuse my (probably) incorrect terminology:
In the following code I don't grasp why you set the containing (parent) div to 'position:relative' in order for the divs inside to be positioned in relation to the parent div (using 'position:absolute). I thought in order for this to happen the children divs would be set 'relative' to the parent. Am I to understand that essentially the parent div is saying to the other divs inside "hey, you can all be positioned 'relative' to me now!" I sort of expected it to work the other way around.
E.g. I expected the text would have been positioned "relative" to the containing div. Can someone explain why it works the way it does here? Thanks.
<div id="backgroundImage">
<h2 class="titleBox">I AM A TITLE</h2>
<p class="textBox">I am a description box</p>
</div>
#backgroundImage {
position: relative;
height: 225px;
width: 300px;
background-image: url (#);
}
.titleBox {
position: absolute;
top: 15px;
left: 0;
}
.textBox {
position: absolute;
bottom: 10px;
left: 0;
}
The documentation explains this very well, but I'll summarize.
An element with position:relative is first laid out just like any static element ... shifted according to the top, bottom, left and right properties
The position: relative box can be adjusted relative to its parent (even if its parent is static).
For position: absolute,
the containing block is the nearest positioned ancestor. By “positioned” I mean an element whose position property is set to relative, absolute or fixed
That is, the top, bottom, etc. properties on a position: absolute element are relative to the nearest containing element of a position other than static (including relative).
That is to say that position: absolute elements can still be positioned relatively.
You position the child elements absolutely, i.e you are specifying x/y co-ordinates for them (using left and top properties).
By default these will be positioned absolutely to the document, but by setting a parent container as position:relative, they will be positioned relative to that div, in an absolute manner.
If you set your element as position 'absolute' it will be out of the DOM.So you can set where ever you want unless or until your absoluted element parent or parents of parent... does not having any position relative.why we use position relative actually is if u want to style the the element irrespectively with other elements inside container, u can set position relative to the parent(means container). If #backgroundImage does not have position relative , your child elements will go initial position of your screen but if u want some where in the middle of ur page u have to styled the "backgroundImage" element as position :relative .. then the child element wil fly inside your "backgroundImage" container.
I have 3 div elements.
1st div is bigger (wrap) and has position:relative;
2nd div is positioned absolute to the 1st div relative positioning (and is included in the 1st div)
3rd div is contained in the 2nd div and also has absolute positioning.
<div id="1st">
<div id="2nd">
<div id="3rd"></div>
</div>
</div>
Why is the 3rd div position absolute to the 2nd div (which is also absolute position to the 1st div) and not to 1st div that has relative position ?
Because the 3rd div is absolute positioning to the absolute positioned 2nd div.
Because position: absolute resets the relative position for children just as position: relative does.
There is no way around this - if you want the third div to be absolutely positioned relatively to the first one, you will have to make it a child of the first one.
Both position:relative and position:absolute establish containing elements as positioning ascestors.
If you need div 3 to be positioned based on div 1 then make it a direct child of div 1.
Note that position: relative means the element is positioned relative to its natural position and position: absolute means the element is positioned relative to its first position:relative or position:absolute ancestor.
Position static: the static position is the default way an element
will appear in the normal flow of your
HTML file if no position is specified at all.
Important: top, right, bottom and left properties HAVE NO EFFECT ON A STATICALLY
POSITIONED ELEMENT.
Position relative: positioning an element with the relative value keeps the element (and the space it occupies) in the normal flow of your HTML file.
You can then move the element by some amount using the properties left, right, top and bottom. However, this may cause the element to overlap other elements that are on the
page—which may or may not be the effect that you want.
A relatively positioned element can move from its spot, but the space it occupied remains.
Position absolute: applying the absolute position value to an element removes it from the normal flow. When you move the absolute positioned element, its reference point is the top/left of its nearest containing element that has a position declared other than static—also called its nearest positioning context. So, if no containing element with a position other than static exists, then it will be positioned from the top-left corner of
the body element.
In your case 3rd's nearest containing container is 2nd.
Yet another clarifying answer.
Your current scenario is this:
#my-parent {position: absolute}
#my-parent .my_child {position: absolute}
And you're kind of struggling with it.
If you can change the HTML, simply do this:
#my-parent {position: absolute}
#my-parent .my-wrapper {position: relative} /* Since you've added the wrapper in HTML */
#my-parent .my-wrapper .my-child {position: absolute} /* Now you can play with it */
The reason why the 3rd div element is absolutely positioned to the 2nd div element is because as the CSS spec explains here, is because the "parent" element (better said: containing block) of an absolutely positioned element is not necessarily its immediate parent element, but rather its immediate positioned element i.e. any element whose position is set to anything but static for example position: relative/absolute/fixed/sticky;
Hence, whenever possible in your code, if you want the 3rd div element be absolutely positioned in regards to the 1st div you should make your 2nd div element as position: static; which is its default value (or just simply remove any position: ... declaration in the rule set of your 2nd div element).
The above will make the 1st div the containing block of the 3rd absolutely positioned div, ignoring the 2nd div for this positioning purpose.
Hope it helps.
In case anyone is still looking for an answer to this.
I was able to achieve this result by adding a clear: both; style to the first absolutely positioned div which reset the child and allowed it to use it's own absolute positioning.