cascading order = the most specific css-selector is applied! Less specific selectors will be overriden.

1. tagname: least specific
2. class: more specific, recurrent styling
3. id: most specific. One element per id only, applying the same id to multiple elements is invalid HTML and should be avoided

/* tag-level */
body { }

/* class-level */
#myClass { }

/* id-level */
.myId { }