Checks that stylesheets (style attributes, style elements, external style sheets) are case-insensitive, unlike presentational attributes.
Subtest a checks that the invalid attribute FiLl is ignored. Subtest b checks that the style attribute is applied, the values being case-insensitive. Subtests c and d check the same for style elements and imported external style sheets.
Run the test. No interaction required.
If any red shows, the test fails. If four orange circles are shown, the test passes and the user agent supports CSS style sheets. If the top two circles are orange while the bottom two are blue, and the user agent does not claim to support CSS style sheets, the test also passes.