Techniques for WCAG 2.0

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# C12: Using percent for font sizes

## Applicability

CSS

This technique relates to:

- Success Criterion 1.4.4 (Resize text)
  - How to Meet 1.4.4 (Resize text)
  - Understanding Success Criterion 1.4.4 (Resize text)

## User Agent and Assistive Technology Support Notes

When font size is specified in any absolute units of measurement, such as points or pixels, the Text Size menu commands in Internet Explorer 7 and earlier do not resize the text.

When High Contrast Mode has been set from the Accessibility Control Panel on Windows, IE6 increases the size of the page text as if a percentage change had been set for the outermost window via CSS. Standard CSS layout behavior causes relative scaling to be multiplied, so the scaling of text within elements will be different in subtle ways. Firefox and IE7 do not change the scaling of the content based on the system settings in a way that affects CSS layout, so this effect does not occur in those browsers.

## Description

The objective of this technique is to specify text font size proportionally so that user agents can scale content effectively. 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: Percent font sizes in CSS

This example defines the font size for the `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 emphasized words in this example will each be larger than their surrounding text.

Example Code:

    strong {font-size: 120%}

    ...

    <h1>Letting the <strong>user</strong> control text size</h1>
    <p>Since only the user can know what size text works for him,
    it is <strong>very</strong> important to let him configure the text size.
    …

## Resources

Resources are for information purposes only, no endorsement implied.

- Cascading Style Sheets, Level 2 (CSS2), Fonts

- CSS 2 Font Size Property

- CSS-Discuss Font Size Using Percentages

## Related Techniques

- C13: Using named font sizes
- C14: Using em units for font sizes

## Tests

### Procedure

1. Examine all CSS properties that define font size for each rule set.

2. Check that the value is a percentage.

### Expected Results

- Check #2 is true

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