A small anecdote on some CSS usage which tripped me up a few days ago; it’s easy to get carried away and set all your color/background-color properties using the fancy-pants new RGBA. But only do so if you really need to specify the opacity value.
i.e. if you’re setting something like this: color: rgba(213, 265,17, 1);, set it as plain old RGB: color: rgb(213, 265,17);. The latter will render fine in IE, as far back as I was able to test (IE 7, I think), whereas the former only works in newer browsers (IE9+, Firefox, Webkit, Opera).
The “doh!” moment for me came when testing a stylesheet a few days ago. The layout worked fine, but for a moment I couldn’t think why none of the colours were displaying in IE8, until then I remembered I was using RGBA for everything. So off I went to create override classes for IE8, using Modernizr‘s .oldies class. I was about 3/4′s the way through the stylesheet when I realised 99% of the colours I was overriding had no opacity set (i.e. opacity value of 1), and so I could just specify them as RGB. Cue much slapping of the forehead! Lesson learned, and needless bytes saved.
