The css of a major site I am looking at has what appears to be a strange way of managing their font sizes in CSS. First, the body selector has this:
body {
font:62.5%/1.5 Helvetica,Arial,FreeSans,sans-serif;
}
Then later on to get a custom size for the h2 font they do:
h2 {
font-size:3em;
}
If you change the font directives in either of these places, the font size of h2 will change and look incorrect. So they are clearly managing the font size via the combination of these directives, and I want to know why they would do it this way....
Questions:
Why is the h2 font not simply over-riding the body font? It's like the body font is acting as a multiplier on its size....
What is the motivation for this design?
Thanks,
Jonah
Why is the h2 font not simply over-riding the body font? It's like the body font is acting as a multiplier on its size....
Because in CSS, em is a relative unit of measure. Thus 3 ems of 62.5% of the base size means 187.5% of the base size for <h2> elements.
What is the motivation for this design?
Setting a percentage value for the body element means that — % being a relative unit of measure too — the user can resize text in an entire page using his browser's text size setting. I would guess that a value like 62.5% is in case the browser default font size makes the entire body copy too large (remember that this is being applied on the body element). My site uses 90%, which isn't that small but you get the idea.
1em is equal to the default font size. The default text size in browsers is 16px. Unless you change the default, that is.
Here the default is being defined as 62.5% of the browser's default, with a line height of 1.5.
3em is 3 times the default size set.
So when you change the body default it affects every place the em size unit is used, including the h2 tag with is 3 time the default setting.
Usually the browser defines a default font size of 16px. em however, is a relative unit. So for example, if you have a setting a font size for a container/div of
1 em = 1 times 16px = 16px
1.5 em = 1.5 times 16px = 24px
2 em = 2 times 16px = 32px
Therefore by setting it to 62.5%, it reduces down to your reference font size to 10px default.
which means this technique makes it easier when you are visualizing your font sizes in px,
1 em = 10px
1.5em = 15px
2em = 20px
Related
I have two sites on which the font is set by
* {
font-family: "Varela Round", sans-serif;
}
Since the font-size is not specified, the browser use his standard values for each element. But if I set the size to 0.9em the size is really small. The output of window.getComputedStyle(element).fontSize also shows different px values. If I set font-size: 13px the size is everywhere the same.
But if I set the size to 0.9em the size is really small.
Yes, it is a relative size.
The body becomes 90% of the font size of the html.
A section inside the body becomes 90% of the body (so 81% of the html).
A p inside the section becomes 90% of the section (so 72.9% of the html)
And so on.
If I set font-size: 13px the size is everywhere the same.
Absolute units do not vary based on the font size of the parent element.
This explanation is summarized from the site Css Font Size
The reason for this is the fact, that px is not relative to other elements. % and em instead are relative to their parent which results in the following effect:
Since 100% = 1em the two units can almost (see % vs em) be used analogously.
One solution is to use rem, which acts similar to em but does not inherent the value from the parent.
An other is to set a default size for the main element e.g. body and then set the font-size relative to the parent for all elements.
If I dont set my font size, or I set it to 1em I get a computed font size of 16px.
If I set it to .875em I get a computed size of 7px
That doesnt make sense to me.
Its calculation depending on font size set in body tag or browsers default that is 16px size. See below link for detail.
http://v1.jontangerine.com/silo/css/pixels-to-ems/
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.
em adjust size according to screen size,
yes but confused
does em depend upon browser settings? which settings?
or does em depend upon screen resolution?
or help what does it depend upon and from where can these elements be changed to observe the difference in sizing when "em" is used
1em is equal to the current font size. 2em means 2 times the size of the current font. E.g., if an element is displayed with a font of 12 pt, then '2em' is 24 pt. The 'em' is a very useful unit in CSS, since it can adapt automatically to the font that the reader uses
Quote from w3schools
The tricky thing to remember about em as a unit of size when coding CSS is that it is cumulatively relative and, once a base font size has been established, treated roughly like percentages.
Thus picture a <strong> inside a <p> like so:
<p>foo <strong>bar</strong></p>
with the following rules:
p {font-size:0.8em;}
strong {font-size:1.0em;}
Contrary to first impressions, the word bar will not be bigger than the word foo; the words will be the same size - the font size inside the strong tag is set to 1.0 em relative to 0.8 em, or 0.8 em.
By the same token rules like so:
p {font-size:0.8em;}
strong {font-size:0.8em;}
Will not result in foo and bar being the same size; foo will be 0.8em relative to it's container's font size while bar will be 0.8em relative to it's container's font size, or ~0.64em relative to foo's container.
or more exactly, a em is the height/width in pixels of a "M" character in the current font-family/font-size. unless it's a monospace font, a "|" and a "M" represent different widths in pixels...
em is related to the current font size - as set by css on parent elements. Historically em was taken as the width of the letter M. However since not all fonts include M now that cannot be guaranteed!
The good thing about it is that it will make non-text elements scale with font size if the user changes the font size using their browser settings.
As quoted for w3schools, the em is the "current font size" and everywhere you see 'em' it can be replaced, as to meaning, by the words "current font size".
font-size is 20px then 1 em is 20px. (current font size is 20px).
font-size set to 0.7 em then the font size changes to 14px. (0.7 x current font size = 14px) and one em is now 14px.
If browser default font size is 16px, and font size not set, then:
current font size = default font size = 16px = 1em.
If browser default font size is set to,say, 30px then:
current font size = default font size = 30px = 1em
Screen dpi exists to translate lengths specified in inches into pixels so when font size is specified in points.
font size in pixels =[( font size in points)/72] x screen dpi
To that extent the em depends upon screen resolution i.e. the screen dpi set via the Control Panel.
http://www.emdpi.com/screendpi.html
For computers the em was never the width/height of the letter 'M".
I am still not clear what does size in em mean?
I have worked px, pt in CSS.
What would 0.8, 1.0 and 1.2 em mean?
I have seen height's in CSS like:
height: 0.8em; or height: 1.2em;
How is it calculated?
The meaning of "em" has changed over the years. Not all fonts have the letter "M" in them (for example, Chinese), but all fonts have a height. The term has therefore come to mean the height of the font – not the width of the letter "M."
Let's look at a simple example where we use the em unit to set font sizes:
<html>
<style>
h1 { font-size: 2em }
</style>
<body>
<h1>Movies</h1>
</body>
</html>
When used to specify font sizes, the
em unit refers to the font size of the
parent element. So, in the previous
example, the font size of the h1
element is set to be twice the font
size of the body element. To find what
the font size of the h1 element will
be, we need to know the font size of
body. Because this isn't specified in
the style sheet, the browser must find
it from somewhere else – a good place
to look is in the user's preferences.
So, if the user sets the normal font
size to 10 points, the size of the h1
element is 20 points. This makes
document headlines stand out relative
to the surrounding text. Therefore:
Always use ems to set font sizes!
More Info
1em is equal to the current font size.
2em means 2 times the size of the current font.
E.g., if an element is displayed with a font of 12 pt, then '2em' is 24 pt. The 'em' is a very useful unit in CSS, since it can adapt automatically to the font that the reader uses
Here's a link to other CSS units:
http://www.w3schools.com/cssref/css_units.asp
1em is equal to the current font size. 2em means 2 times the size of the current font. E.g., if an element is displayed with a font of 12 pt, then '2em' is 24 pt. The 'em' is a very useful unit in CSS, since it can adapt automatically to the font that the reader uses.
more here
Paul is correct, however its "M" not "m". However this is an esoteric definition derived from typesetting/printing and isnt of much use in this case. In terms of whats going to be useful to you you its a percentage of font size.
An em is the width of the letter "m" (in your current font and size).
Em is the size of a character. It will vary depending upon the font size. If the font size is 24 then 2Em will be equal to the space it should take to hold two characters of the font size 24.
As quoted from wiki.
An em is a unit of measurement in the
field of typography. This unit defines
the proportion of the letter width and
height with respect to the point size
of the current font.
FYI:
En is half of Em. 0.5Em
An em means "ephemeral unit" it is relative to the current font size of its parent element. For instance, the text in an <h1> heading is 2em by default. This comes from the fact that an <h1> inherits its text size from its parent element, the <body> of the document. If I set my <body> font-size to 16px (font-size: 16px;). My <h1> being 2em would inherit a size of 32px, because 2em is twice the size of 1em. In this case 1em=16px so 2em=2x16px=32px. Now if you create an HTML document with the following
<body>
<h1>Hello world</h1>
<p>Lorem ipsum</p>
</body>
Then you define following CSS rule.
body {font: normal 16px Arial, Helvetica, sans-serif;}
Open the page in a web browser (Chrome) and open the browsers development tools (ctrl+shift+I), you'll see the default font-size for an <h1> is 2em. You will also see on the styles tab that it is "Inherited from body".
While still in the Development Tools for this scenario you can see on the Box Model diagram that the <h1> margin is 21.440px on the top and bottom margins. If you look in the CSS defaults for <h1> you can see the margin-block-start: 0.67em; and margin-block-end: 0.67em; Remember sizing is relative to the font size of the parent element, so 0.67em is relative to the <h1> font size not the font size of the <body>, you can verify this with a little math, 0.67em x 32px=21.440px and this is the size of the margin of the <h1> in the Box Model diagram. For more information try http://www.123webconnect.com/convert-px-em.php