Technique C14:Using `em` units for font sizes

About this Technique

This technique relates to:

1.4.4: Resize Text (Sufficient when used for techniques for relative measurements)
1.4.5: Images of Text (Advisory)
1.4.8: Visual Presentation (Sufficient when used with G146: Using liquid layout)
1.4.9: Images of Text (No Exception) (Advisory)

This technique applies to CSS.

Description

The objective of this technique is to specify text font size in em units so that user agents can scale content effectively. Since the em is a property of the font, it scales as the font changes size. If a font-size is specified for the body element, all other elements inherit that value, unless overridden by a more specific selector.

Examples

Example 1: `em` font sizes in CSS

This example defines the font size for strong element so that its text will always be larger than the surrounding text, in whatever context it is used. Assuming that headings and paragraphs use different font sizes, the strong words in this example will each be larger than their surrounding text.

<style>
  strong {font-size: 1.6em}
</style>
...	
<h1>Letting the <strong>user</strong> control text size</h1>
<p>Since only the user can know what size text works for them, 
   it is <strong>very</strong> important to let them configure the text size.</p>
…

Related Resources

No endorsement implied.

Tests

Procedure

Check that the value of the CSS property that defines the font size is expressed in em units.

Expected Results

Check #1 is true