覆盖用户代理CSS样式表规则的最佳方法是什么，该规则为无序列表提供1em余量？

I'm working on a web app that has a topBar similar to facebook's blue bar at the top. I have an unordered list within the div of that bar to list some items, like Inbox, Notifications, etc. The UL has a 1em margin as defined by the user agent stylesheet of my browser. This is a problem because it's pushing my topBar down 1em. How can I override this to make the border of the ul = 0? I've read that overriding user agent stylesheets is a bad idea so I'm curious to learn what is best to do. Thanks.I'm working on a web app that has a topBar simi