Many HTML elements have presentation attributes, which get translated into CSS properties that get inserted into a particular place in the cascade:

"The UA may choose to honor presentational attributes in an HTML source document. If so, these attributes are translated to the corresponding CSS rules with specificity equal to 0, and are treated as if they were inserted at the start of the author style sheet. They may therefore be overridden by subsequent style sheet rules."

http://www.w3.org/TR/CSS2/cascade.html

I don't know of any way currently for a web component to insert presentational CSS into the correct place in the cascade.