tabstrip - Underline selected header

I have a request to underline the selected header of the Ajax control toolkit tab strip.  I have added the text-decoration: underline to my css for the selected tab as shown:

.MyTabStyle .ajax__tab_active .ajax__tab_inner {
text-decoration: underline;
font-size: 15px;
font-weight: bold;
}

Unfortunately, the underline text-decoration is not being honored.  Any suggestions are appreciated.  TIA.

Wally