Tabs

Use this in usechrome.css

/* Change color of active tab */
tab[selected="true"] {
-moz-appearance: none !important;
background-color: #FFFFFF !important;
border-left: solid 1px #FF0000 !important;
border-bottom: solid 2px #232423 !important;
color: #000000 !important; }

/* Change color of normal tabs */
tab:not([selected="true"]) {
background-color: #EBEBEB!important;
border-left: solid 1px #0066CC !important;
border-right: solid 1px !important;
border-bottom: 2px solid #615F5F !important;
color: black !important; }


Chane the colors as per need and for your problem you will need to change the border bottom color :)