Change background color of active tabs

Using Bootstrap v2.3.2, I am trying to change the default background color for the active tabs. I've tried to set as below, but it doesn't work:

.nav-tabs > .active > a,
.nav-tabs > .active > a:hover,
.nav-tabs > .active > a:focus
{
    color: #555555;
    background-color: red;  
} 

Any advice as to why this isn't working, or how to fix it?