You always have to worry about supporting some of those legacy browsers. Nothing is worse than pesky ol’ IE. It has gotten better now… a bit. In the latest project I have worked on we are supporting IE9+ and the “other browsers” (because they just work).
We set out to make a nice change in our application to increase modularity and break down our CSS files (actually using LESS), into very small chunks each related to their own script component and template. This means you can make a style change knowing you are not going to touch anything other than that component (it is not shared, etc). This is a pretty standard practice nowadays and simplifies testing greatly… and all around I feel a lot better about making more drastic changes at this level of granularity. Once our application hits release mode, everything is automatically bundled and minified so we don’t need to worry about loading 40 individual style sheets from the client.
This is something that you should definitely be aware of in case it ever bites you!
See this and more limitations on maximum number of CSS rules here: