As I write the styling for a new site, I want to pay careful attention to too much CSS. As a result, I did some searching on layout times and came across a list of CSS Selector types ordered from most efficient to least efficient. Here they are:
- ID, e.g.
#header - Class, e.g.
.promo - Type, e.g.
div - Adjacent sibling, e.g.
h2 + p - Child, e.g.
li > ul - Descendant, e.g.
ul a - Universal, i.e.
* - Attribute, e.g.
[type="text"] - Pseudo-classes/-elements, e.g.
a:hover
Not surprisingly, something like #myid is the fastest. More information can be found here: http://csswizardry.com/2011/09/writing-efficient-css-selectors/