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Technique C14:Using em units for font sizes

About this Technique

This technique is Sufficient to meet 1.4.4: Resize Text and Advisory for 1.4.5: Images of Text and Sufficient to meet 1.4.8: Visual Presentation when used with G146: Using liquid layout and Advisory for 1.4.9: Images of Text (No Exception) .



This technique relates to:


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.


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.

  strong {font-size: 1.6em}
<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>

Other sources

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

Expected Results

  • Check #1 is true
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