The mighty developer console will be your saviour! F12 in most browsers, although you can invoke it directly by right-clicking the problem element, then selecting “inspect” from the context menu. When that’s visible, use the main pane to drill up/down the HTML, and the styles pane on the right to tweak your CSS. You can edit it live in the browser, then when you’ve got your modifications looking nice, transfer them to your stylesheet. CSS selectors will be shown in the styles pane (along with related stylesheets) to help guide you on your quest.
Good luck with your project.