Let's say that end user has issues reading smaller text, so they've set their browser to default to 20px. If I set the rem size like this:
html {
font-size: max(1rem, 2.5vh);
}
Will it override their preference, or would it set "rem" to their preference (20px, in this case)? I don't want to break accessibility, but also want to scale the font with the screen-size. It seems to work on my end, but I want to be sure this is the best method.
"rem" refers to computed value of font-size of the root element, so the result of the font-size: max(1rem, 2.5vh); setting.
1rem applied to the font-size of the root element = 1em, so the rem size is the result of max(20px, 2.5vh) if the user has set the default to 20px.
To cite MDN on the <length> unit rem
rem
Represents the font-size of the root element (typically <html>). When used within the root element font-size, it represents its initial value (a common browser default is 16px, but user-defined preferences may modify this).
The CSS unit rem is short for “root em”. When used in CSS 2rem evaluates to “two times the font size on the root element” which in an HTML document is two times the font size on the HTML element. I know that I can change the font size on the HTML element by specifying it in e.g. html { font-size: 10px; }. But does it make any sense to do so using rem units? What does it even mean? Does the spec say?
If font-size is not specified, browser will use the default size (which is in most cases 16px, but I can't find it being specified anywhere in the CSS specification).
Now what using rem in root element will do is using that default value and multiplying it, 1rem = 16px, 2rem = 32px.
The spec seems to confirm that: https://www.w3.org/TR/css-values-4/#rem
rem unit
Equal to the computed value of font-size on the root element. When specified on the font-size property of the root element, the rem units refer to the property’s initial value.
I wouldn't say it makes any sense, since relying on browser's default values in CSS isn't necessarily a good idea, but if you want to multiply the browser's default font size you can.
I already searched and read SOF on this topic, I found some posts interesting, particularly one that suggested to use pt for font-size because it is neither related to the pixel density, nor to the resolution, but I'm still in search...
Is there any way so I could define a specific font size in my css document, but use it with proportion to the default font size of the browser? something like this:
x = default-font-size-of-browser %
unit-to-use = (x) / (my-target-size%) em
then use that for every padding, margin, etc. in the design, which is not possible in css as long as I know!
I've found people guessing like "usually, the default of browser is 16px font-size", I don't want to guess.
Some suggested to use 100% for html tag and define all other sizes with rem: now what if the user has a wrong font size as default of the browser? Then the user will see all sites that have that overwritten well, except my site, that is not overwriting it! Sure I can think of that as being the user's problem and leave it on, but I won't take that way.
Please give ideas.
Generally, you should not change the font size of body text. The user has configured his browser to suit his display and his eyesight. If you force the font size to something else, the user may not be able to read the text.
Option to use pt as unit to define font size is meant to be used with printers, but it is not good idea to use it for screen. It tries to set absolute size ( 1pt=1/72in). Even if the text is correct size on your desktop PC, it is most likely not correct on a small phone screen. (A phone screen is viewed from shorter distance, so the font needs to be smaller.)
In addition to that, pt size depends on the dpi setting on users computer. Many users have wrong dpi setting (it depends on the monitor used), so the size of the font will not be what you expect.
The unit px is not good since the size of pixels wary between displays, as does users eyesight. However, it is useful if you want the text to be aligned correctly with an image, since the image (when displayed in actual size) is dimensioned as pixels.
In most cases, the size of body text should be 100% (i.e. do not change it). For other elements, use relative sizing (e.g. as %). If you must change the font size for body, the other elements will automatically change relative to that. The size given as % is size relative to the font size on parent element.
The default font size is the same in every browser, AFAIK.
The common suggestion for font size is:
body {
font-size: 62.5%;
}
This sets the base font size to 10px, but with scaling.
Then lets say for example you want the text of your website to be 16px, you do:
p, ul, ol, table {
font-size: 1.6em;
}
And then to set your headings:
h1 {
font-size: 2.5em;
}
h2 {
font-size: 2em;
}
For 25px and 20px respectively.
This method means that even if the default font size isn't as you would expect, the text should still scale accordingly.
See this other post by me for some cool things you can do with fonts and font sizes. Works well with responsive layout
I'm having trouble writing maintainable CSS code when font size is specified with EM units as opposed to PX units. I've been accustomed to writing CSS code like this:
body {font-size: 12px;}
body .sidebar {font-size:11px;}
body .sidebar .loadmore {font-size:10px;}
body .sidebar .warning {font-size:13px;}
The idea is that on many pages through out the site, there's a lot of text that should have 12 pixel font-size. I take advantage of the rules of specificity to override the 12px font size in special areas of the site.
Let's say I rewrote the above code as:
body {font-size: 12em;}
body .sidebar {font-size:11em;}
body .sidebar .loadmore {font-size:10em;}
body .sidebar .warning {font-size:13em;}
If I replaced px with em in the code above, my understanding is that I lose the advantage of rules of specificity. Line 3 of the code would be interpreted as " 10 em of 11 em of 12 em" which is not at all the same meaning as " override all previous rules and use 10 em of (what is the default?)". Is what I've stated correct?
edit If what I've said is correct, then how does one write a font size rule such as "use font size X for all elements, but use font size Y on side bars"?
John the specificity that you are talking about will occur in the way that you have stated. A reference as to why can be seen: http://kyleschaeffer.com/best-practices/css-font-size-em-vs-px-vs-pt-vs/.
Edit As a reply to your edit please consider what jnylen posted in the comments of your original post.
A font size of 12 em as you have listed for body {font-size: 12em;} is going to scale the default font size to 12x it's current size. If you would like to use em's you need to consider at what scale rate you wish to use them and do the math. If you want to set fixed sizes with nested statements you need to stick to fixed attributes (pixels). The advantage of em's as stated in the article that I linked is that you can set a default size, say 12 px and then use em to scale them. For example in mobile based websites.
Yes, em values "multiply" together when the elements they apply to are nested. It's not necessarily a specificity issue - if you specified the rules individually for .loadmore and .sidebar you would see the same issue, since .sidebar contains .loadmore.
Here's an example of a way to work with this: http://jsfiddle.net/PJWrW/
I usually use either px or percentage units for font sizes, to make it explicit that I'm setting an absolute font size or modifying the parent font size.
I sometimes use em units for defining dimensions like paddings and widths, since an em unit is basically the width of a letter at the current font size.
As far as I know, if you're using em's for font size, there is no one way to set a standard font size for elements in a left hand side bar (or elsewhere for that matter) whilst setting the specific size of some elements in that side bar. If you use em's you'll have to specify the sizes of all elements in that side bar.
Personally I usually use px for font sizing, simply because you can set a standard font size for certain elements as you say in your post.
The only convincing arguments I have heard for using em over px regard scaling issues that are no longer really a problem (IE6 doesn't allow you to change font size manually if you use px but most people stopped hacking for IE6 a while back) The only real situation I can see using em as an advantage is if you want to implement functionality whereby the user can change the font size via JavaScript like here
There are many articles and questions about percentage-sized vs other-sized fonts. However, I can not find out WHAT the reference of the percent-value is supposed to be. I understand this is 'the same size in all browsers'. I also read this, for instance:
Percent (%): The percent unit is much like the “em” unit, save for a few fundamental differences. First and foremost, the current font-size is equal to 100% (i.e. 12pt = 100%). While using the percent unit, your text remains fully scalable for mobile devices and for accessibility.
Source: http://kyleschaeffer.com/best-practices/css-font-size-em-vs-px-vs-pt-vs/
But if you say "ie 12 pt = 100%", then it means you first have to define font-size: 12pt. Is that how it works? You first define a size in an absolute measure, and then refer to this as '100%'? Does not make a lot of sense, as many samples say it is useful to put:
body {
font-size: 100%;
}
So by doing this, WHAT is the font size relative to? I notice that the size I see on my screen differs for every font. Arial looks way bigger than Times New Roman, for instance. Also, if I would just do this, body size = 100%, would that mean that it will be the same on all browsers? Or only if I first define an absolute value?
UPDATE, SAT JUL 23
I am getting there, but please bear with me.
So, the % value relates to the default browser font size, if I understand correctly. Well, that is nice but gives me again several other questions:
Is this standard size always the same for every browser version, or do they vary between versions?
I ! found (see image below) the settings for Google Chrome (never looked at this before!), and I see standard "serif", "sans-serif" and "monospace" settings. But how do I interpret this for other fonts? Say I define font: 100% Georgia;, what size will the browser take? Will it look up the standard size for serif, or has the "Georgia" font a standard size for the browser
On several websites I read things like Sizing text and line-height in ems, with a percentage specified on the body [..], was shown to provide **accurate, resizable text across all browsers** in common use today. But from what I am learning now I believe that you should actually choose between either resizable text (using % or em, like what they recommend in this quote), or having 'accurate, consistent font-sizes across browsers' (by using px or pt as a base). Is this correct?
Google Settings:
This is how I think things could look like if you do not define the size in absolute values.
The browser default which is something like 16pt for Firefox, You can check by going into Firefox options, clicking the Content tab, and checking the font size. You can do the same for other browsers as well.
I personally like to control the default font size of my websites, so in a CSS file that is included in every page I will set the BODY default, like so:
body {
font-family: Helvetica, Arial, sans-serif;
font-size: 14px
}
Now the font-size of all my HTML tags will inherit a font-size of 14px.
Say that I want a all divs to have a font size 10% bigger than body, I simply do:
div {
font-size: 110%
}
Now any browser that view my pages will autmoatically make all divs 10% bigger than that of the body, which should be something like 15.4px.
If I want the font-size of all div's to be 10% smaller, I do:
div {
font-size: 90%
}
This will make all divs have a font-size of 12.6px.
Also you should know that since font-size is inherited, that each nested div will decrease in font size by 10%, so:
<div>Outer DIV.
<div>Inner DIV</div>
</div>
The inner div will have a font-size of 11.34px (90% of 12.6px), which may not have been intended.
This can help in the explanation:
http://www.w3.org/TR/2011/REC-CSS2-20110607/syndata.html#value-def-percentage
My understanding is that when the font is set as follows
body {
font-size: 100%;
}
the browser will render the font as per the user settings for that browser.
The spec says that % is rendered
relative to parent element's font size
http://www.w3.org/TR/CSS1/#font-size
In this case, I take that to mean what the browser is set to.
A percentage in the value of the font-size property is relative to the parent element’s font size. CSS 2.1 says this obscurely and confusingly (referring to “inherited font size”), but CSS3 Text says it very clearly.
The parent of the body element is the root element, i.e. the html element. Unless set in a style sheet, the font size of the root element is implementation-dependent. It typically depends on user settings.
Setting font-size: 100% is pointless in many cases, as an element inherits its parent’s font size (leading to the same result), if no style sheet sets its own font size. However, it can be useful to override settings in other style sheets (including browser default style sheets).
For example, an input element typically has a setting in browser style sheet, making its default font size smaller than that of copy text. If you wish to make the font size the same, you can set
input { font-size: 100% }
For the body element, the logically redundant setting font-size: 100% is used fairly often, as it is believed to help against some browser bugs (in browsers that probably have lost their significance now).
Sorry if I'm late to the party, but in your edit you make a remark about font: 100% Georgia, which the other answers haven't responded to.
There is a difference between font: 100% Georgia and font-size:100%; font-family:'Georgia'. If that was all the shorthand method did, the font-size part would be meaningless. But it also sets a lot of properties to their default values: the line height becomes normal (or around 1.2), ditto for the style (non-italic) and weight (non-bold).
That's all. The other answers already mentioned everything else there was to mention.
It's relative to default browser font-size unless you override it with a value in pt or px.
As you showed convincingly, the font-size: 100%; will not render the same in all browsers. However, you will set your font face in your CSS file, so this will be the same (or a fallback) in all browsers.
I believe font-size: 100%; can be very useful when combining it with em-based design. As this article shows, this will create a very flexible website.
When is this useful? When your site needs to adapt to the visitors' wishes. Take for example an elderly man that puts his default font-size at 24 px. Or someone with a small screen with a large resolution that increases his default font-size because he otherwise has to squint. Most sites would break, but em-based sites are able to cope with these situations.
According to ALL THE SPECS DATING BACK TO 1996, percentage values on font-size refer to the parent element's (computed) font-size.
<style>
div {
font-size: 16px;
}
span {
font-size: 75%;
}
</style>
<div><span>this font size is 12px!</span></div>
It's that easy.
What if the div declares a relative font-size, like ems, or even worse, another percentage?? See “computed” above. Whatever absolute unit the relative unit converts to.
The only question that remains is what happens when you use a percentage value on the root element, which has no parent:
html {
font-size: 62.5%; /* 62.5% of what? */
}
In that case, see the “duplicate” of this question. TLDR: percentages on the root element refer to the browser default font size, which might be different per user.
References:
CSS 1 spec (1996)
CSS 2.1 spec (2011)
CSS Fonts Level 3 spec (2013)
CSS Fonts Level 3 editor’s draft (2017)
Relative to the default size defined to that font.
If someone opens your page on a web browser, there's a default font and font size it uses.
As to my understanding it help your content adjust with different values of font family and font sizes.Thus making your content scalable. As to the issue of inhering font size we can always override by giving a specific font size for the element.