Start with creating from scratch your own brand spanking new theme, and then applying your own CSS tweaks to it. Step 1: create a zip of your base theme and get me to host it on the server.
Step 2: verify that
it “stjerome_s”(Difficult) or “Toolbox” or “Bones” or “Victoria Park” as the active theme on your site before you commence a-fiddling with it.
Tips: Enable the developer menu in Safari so you can find the needles in your haystack of code.
In 2013 we used “ToolBox” theme – but any other modern theme in the theme menu is doable for custom CSS changes/tweaks. Read more about “underscores” _S theme.
Watch the video, from the point of view of CSS design tips only. You might get some tips on what to change in the CSS: http://wordpress.tv/2013/09/28/steve-zehngut-underscores-the-only-theme-that-matters/