I read a lot of posts here where someone says "I tried that and nothing changed." Occam's razor tells us to try the simplest things first. If you change something, like custom CSS, and nothing happens, try the following:
1. Reload the page. Just because you close the page and reopen it doesn't mean you've gotten the page from the server. Some browsers are very good about pulling pages out of their cache.
2. Better yet, empty your cache and then reload the page. If you don't know how to empty your cache, check the help menu or google it.
3. Disable your caching plugins if you are using them, because no matter how many times you empty your browser cache and reload, until the refresh time has expired, your browser will continue to reload the same html files from the server, rather than requesting that the server generate new ones based on the original php. Until you get a lot of traffic to your blog, you can probably get by without them.
4. Be sure to view your page in different browsers because not all browsers display things the same way, especially if you are running IE. What is often a problem in IE is not a problem for any other browser.
5. Last but not least, be sure to click the "save changes" button before you navigate away from that page. It's easy to forget this, especially if you are tired, frustrated, excited, or a noob. I've been all four things and I've forgotten to do this many times.
Hope this helps. Ken