CSS–101 – Go fetch yourself!

Using descendant selectors is inneficient, but when your key selector (the rightmost selector) is a ID selector, then things get worse.

via CSS–101 – Go fetch yourself!. It’s a little weird sometimes to think that the CSS selectors work from right to left, so if you end with an id, you just spent way more time on grabbing a DOM element, the browser grabbed with the id alone.