I have designed my page yesterday only. I faced the same situation. I found that,suppose you want to design left navigation bar,then right click on that,click Inspect Element.
Find the class that is used there and apply customization to that class. e.g.
Refer to my profile page,i have used
.nav-left {
border: 1px solid #000;
BackGround-Color:#000;
}
for left navigation pan.
Regards..:)