When should I use rem over px? I see a lot of articles saying that I should use REM to respect the user preferences, but the examples always says about font size, not the about the whole style - margin, padding, border, width, height, etc. Took this article of SO as example: Should I use px or rem value units in my CSS?
ALL the answers are saying about the font-size, ok, I get it, rem is better for font-size, but what about the other styles? I see that bootstrap uses px to the container class, to the col-* class, is there a reason for that?
I'm creating this site that overwrites the default styles of Bootstrap, should I overwrite the places where it uses px with pxs or should I use rem?
Thank you.
Before you go into what unit of css you should use. You must have a understanding of the units themselves. Because you are the only one who knows what styling you want for your site e.g. (static, dynamic/responsive). Only you can decide which unit to use. So in order to make the decision, first learn about the types of css units and their advantages. Here is the w3school link explaining all units like em, rem etc.
https://www.w3schools.com/cssref/css_units.asp
Now coming to your point specifically, rem as defined is the font-size set for the root element that is <html>. By default the font-size of the <html> root element is 100% which equals to 16px as set by the browser. It can be changed in the browser setting or you can override it in css with html {font-size: 20px}. Whatever the font-size set of the html tag will equal to 1rem.
Now, You can use rem for padding and margin etc but it is not recommended because e.g. you have set the rem values of padding and margins and widths etc for your site where your browser default font-size is set to 16px. So it all looks well and adjusted but what if a user who is browsing your site has set their default font-size of the browser to 25px. That will break your site's design. So that is why for responsive sites, the units %, vw/vh are mostly used. As for the px unit. They are their to help set static values so that you fix the size rather than have it readjust.
So now you know what size you want to keep your website's. You can use the units as needed.
Hope this helps you in your understanding and again, try understanding the theory itself before taking in opinions of others on that theory. :) Happy coding.
Related
There's quite a lot of resources encouraging to use ems over pixels in media queries. However, none of them easily explains the obvious doubt about it:
If I have two divs and I want to hide one of them on iPhone4-like devices, how do I do it with em-based media queries? The device resolution is 640x960 in pixels.
In every article there a note that usually 1em = 16px. But since it is not certain, why would I want to convert to ems and risk breaking my design? What if user changes his default font to 20px? Or 10px? My div will hide either too soon or too late.
Example from Foundation:
/* min-width 641px, medium screens */
#media only screen and (min-width: 40.063em) { }
How can I be sure it really is 641px and not 1282px? Why would anyone use something so untrustworthy instead of old good pixels?
First the sizing in em cannot be changed by the user as this is a browser setting that cannot be changed. So at best it could vary between browsers but I don't know any that differs from this standard. For that reason, it can be considered quite safe to use.
But for media queries, I would recommend to use rem units. em units is mostly preferred for font sizing in components as it scales relatively based on the parent DOM element. While rem units work well for sizing root elements (width, height...).
px is an absolute unit of measurement (like in, pt, or cm) that also
happens to be 1/96 of an in unit. Because it is
an absolute measurement, it may be used any time you want to define
something to be a particular size, rather than being proportional to
something else like the size of the browser window or the font size.
em is not an absolute unit - it is a unit that is relative to the
currently chosen font size. Unless you have overridden font style by
setting your font size with an absolute unit (such as px or pt), this
will be affected by the choice of fonts in the user's browser or OS
if they have made one, so it does not make sense to use em as a
general unit of length except where you specifically want it to scale
as the font size scales.
Based on this, the most accurate option is using px instead of embased on what you are asking, but you can always redefine your fonts and use rem instead, this is better for responsive websites, together with percentages. That's a matter of judgment in every single element you are adding to your website, and of course, lots of testing to make sure it looks good and works flawless on any resolution and devices.
I personally prefer to do it this way:
I define my fonts and font-sizes (this overrides the default ones)
I use percentages for the block elements
I use rem for the fonts and media queries
But of course sometimes I have to use pixels or change some of my "default" rules depending on my needs. As I said before, it's too a matter of judgement on your needs and on it is best.
Note: The em unit is relative to the font-size of the parent. The rem unit is relative to the root—or the html—element. That means that we can define a single font size on the html element and define all rem units to be a percentage of that.
I am aware of vw units, however, these are based on the size of the viewport, i.e., the entire screen. What if I need a font-size to be large enough to fit a particular width of a div.
Is that possible?
Any solution or workarounds if it's not?
Thanks!
I agree with user1902183 that there is no need to downvote this question as its perfectly legitimate.
I would suggest taking a look at the rem unit.
rem stands for relative em.
As most developers know, an em is fixed according to device. For example, in a browser 1em = 16px. On mobile devices this may be a smaller figure.
With a relative em the font size is dependent on the parent I believe but investigate this. This may be the closest to what you are trying to achieve without resorting to JavaScript.
I really googled a lot but I can't find a clear answer. I want to use rem which according to the specs
The rem unit is relative to the root—or the html —element.
So my question is:
Does the <html> tag's font-size attribute override the browser's default font-size?
Is it reliable to set my element's rem based on that assumption?
e.g. Some users from China have set their browser's default font-size to 12px, while the users from Europe usually have 16px. I want my designs to scale correctly for both. If the <html> tag contains this setting it would be relatively easy to do scalable designs using rem.
I may not have understood your question completely, in which case I apologise.
Anyway, I hope this helps.
1rem is equal to the font size of the html element. No matter if your stylesheet assigns a font-size to html or not.
So for example, if a user has 15px for a default font size, then a stylesheet saying
div {font-size:2rem}
will display all divs with a font size of 30px.
If, on the other hand, you have this for a stylesheet
html {font-size:12px}
div {font-size:2rem}
then 1rem will be 12px, and all divs will display at 24px, regardless of the user's default font settings.
html {font-size:12px;}
div {font-size:2rem;}
This is normal size text
<div>This is a div</div>
So if you want 1rem to remain at the user's preferred size, but still want to display most of the website at a size of your choice, the trick is to not change the font size for html, but only for body.
body {font-size:12px;}
div {font-size:2rem;}
This is normal size text
<div>This is a div</div>
Disclaimer: If you do change the html font size in your stylesheet, the user settings for "minimum font size" may mess things up.
Also note that you will only see the difference between these two snippets if your own default font size is not 12px!
I've been using px for almost all the measurement related styling, but I wanted to know the best places for the use of pixels (px), percentage (%), points (pt) and em.
I've seen the use of em and (I believe) points in typography, but I don't know the best way to use them.
Where should either be used, and why?
pt or cm, in, mm etc. are most used for print stylesheets, as they're most fit for measurements on the physical properties of paper sheets, and the render of printers.
em and en (and the new rem, and more interesting units such as ch) are glyph relative units, and as such are suitable for text styling, in correspondence with absolute units at the root element (e.g. px units at the body).
another interesting uses: ex units (the height of the 'x' glyph in the font) to set vertical measures in relation to text, ch to indent lines.
px are absolutely rendered so one can design a pixel-perfect (or fixed) layout based on these units, applied for containers, or on various widgets demanding fixed size (buttons and the like). disclaimer: absolutely is an over-statement, as pixels are rarely absolute, and has many factors affecting the rendered outcome - see this article about px as an angular measure.
% are mostly used in conjunction with an absolute unit at the top container, and are applied in various CSS techniques, such as the faux centered container. these units are also very handy for layouts that are fluid by nature. others, like the viewport relative vh, vw and vmin, may be used regardless of the parent's units.
all of the above is based on my personal views, as this subject is open for debate, and CSS techniques will keep evolve and we'll see more uses of the specifications and capabilities we had never thought of. it's mostly the creative use of those tools that scopes or favors the use of one unit over another.
It used to be that these distinctions mattered: for example, back in the IE6 days, you should never set your text using px, because then it couldn't be zoomed. That is, back in the day, browsers actually treated px as a number of pixels.
These days, browsers have conformed to web reality: most people use px everywhere, for almost everything. Thus px is now defined as an angular measurement, which essentially means that px behaves just fine in any zoom setting and on any size or DPI device.
Similarly, as part of conforming to web reality, all other units are defined in terms of px, so there is really no reason to use them unless it happens to be more convenient for your case. The only exception is, of course, percentages, since they allow you to specify values in relation to parents' measurements.
Details from the spec:
in, cm, mm, pt, and pc are all defined relative to px, since in practice all devices follow "For a CSS device, these dimensions are ... anchored ... (ii) by relating the pixel unit to the reference pixel." And as discussed, the "reference pixel" is an angular measurement that varies depending on DPI settings, screen size, zoom level, device type and so on.
1em equals the computed font-size of an element, which is usually defined in px. If that size itself is defined in ems or exs, the browser then looks upward until it finds a px to be relative to, eventually falling back to the default font-size (usually 12px).
1ex equals the height of the letter "x" in the defined font-size if possible, but usually (?) falls back to 0.5em.
Use px for elements that are of a set size.
Use percentage when you need the element to be in proportion to the window size or parent element size.
em is the standard for text, it adjust according to screen size on a mac. Make it a habit, there's plenty of good blogs on why to use em, em is not just for font properties it also comes in handy with other elements like div, inputs etc. There may be consequences when using px for font size, there's also situations where px and % will be more ideal, it' takes trial & error to understand fully.
There are no real rule on what to use it's all according to the desired effect. As you create you will test your site in different resolutions and adjust the browser size to see how it appears from a variety of users points of view.
Consider cross browser compatibility & resolution with em,
Consider resolution with percentages,
Disclosure: I am a sysadmin, not a web designer.
I generally use em for padding around images, so as to keep the padding sized according to the text it keeps away from the image.
I use % to handle liquid/fluid layouts sometimes, though most often a fluid layout will just be 100% of the browser but with fixed width (px) columns.
I use px to handle column widths, headers, etc. The height and width attributes of an <img> tag are of course in pixels by default, and an image will render best if you don't ask the browser to resize it from its native/original resolution. In some cases, you need to use px on fonts, when the font has to work with an image (i.e. a spanner icon next to the word "Tools"). If possible, I always use UTF-8 fonts instead of images.
As you know, you can specify dimensions with CSS in px or em. As far as I understand it, em means "line height of the current element's fonts". My approach currently is to always use px (also for margin which seems to be a controversial practice).
Question: Can I rely on the ratio of px and em to be the same across browsers? If not, then my manually specified margins between paragraphs will likely look odd because they so not match 1em anymore.
I believe that it is better to use em for margins but I have quite a base of existing code that always uses px margins.
No. ems are relative to the user's chosen font size, px aren't. The default font sizes of desktop browsers are about the same in pixels, but mobile devices in particular will vary even before user adjustment.
You should use em for a margin in text content that should be sized similarly to the surrounding fonts, and px for a margin that has to line up with images used by the page layout.
No, you cannot.
The size of em in pixels is related to the font type & size you're using, the resolution of your screen (depending on OS, browser), and possible further OS and browser settings - eg "Show fonts +10%" may alter the em value.