Explicit space must be displayed around any text.
Background under the text must not be distorted by any colored interface (frame, background change or content of other element, document border) in sufficient distance from the text's edge (that means that text must not be "sticked" to the border's edge, document's border nor to any other element).
The vertical distance between adjacent text blocks (i.e. paragraphs) must be bigger than line spacing of those blocks. In horizontal direction the distance must be at least two times bigger than spaces between words.
Only absolute sizes or relative units may be used to define the font size, ...
Author may only define the font size absolutely (by CSS keywords xx-small, x-small, small, medium, large, x-large and xx-large), or relatively to the font size of another element (values smaller, larger, per cents and em and ex units). Absolute units (pt, cm, mm, in, pc) may only be used on pages medias (i.e. for print). The font size must not be specified in px unit.
... and the font size should not be smaller than xx-small.
This restriction applies even to relative font size, authors must respect following table:
| CSS sizes ratios | xx-small | x-small | small | medium / default |
large | x-large | xx-large |
|---|---|---|---|---|---|---|---|
| xx-small | 100% | 125% | 148,33% | 166,67% | 200% | 250% | 333,33% |
| x-small | 80% | 100% | 118,67% | 133,33% | 160% | 200% | 266,67% |
| small | 67,42% | 84,27% | 100% | 112,36% | 134,83% | 168,54% | 224,72% |
| medium / default |
60% | 75% | 89% | 100% | 120% | 150% | 200% |
| large | 50% | 62,5% | 74,17% | 83,33% | 100% | 125% | 166,67% |
| x-large | 40% | 50% | 59,33% | 66,67% | 80% | 100% | 133,33% |
| xx-large | 30% | 37,5% | 44,5% | 50% | 60% | 75% | 100% |
Example: When an element is set to have a size of large, the value xx-small refers to 50 % of its size. From the large size must therefore not be derived font smaller than 50% (that is 0.5em). When the element's size is not specified, it is assumed, that default font size is medium.
Small font sizes are used only rarely, for subsidiary document's elements. The font size of the document's convey must be at least small.
Typefaces when specified for screen or print media stylesheets must include an option certain to be available on the user's output device (usually handled by including a generic type).
The last value of font-family in CSS definition must be one of the following values: serif, sans-serif, monospace, cursive or fantasy.