Menu Colour Code Confusion

Ok can someone advise me on what is going on with this theme. I have the following code to change the tab colour and the the line underneath the tabs also.

　　　
　　　.themonic-nav li:hover {
　　　background-color: #6AA121;
　　　}
　　　 #searchsubmit {
　　　 background-color: #6AA121;
　　　 color: #6AA121;
　　　}
　　　 .themonic-nav .current-menu-item > a,
　　　 .themonic-nav .current-menu-ancestor > a,
　　　 .themonic-nav .current_page_item > a,
　　　 .themonic-nav .current_page_ancestor > a {
　　　 background: none repeat scroll 0 0 #6AA121;
　　　 font-weight: bold;

I had everything in custom css pluggin and the colour changed when on a tab, but didn’t change the line underneath the tabs. Then i was given a code to change that, the code is:

.themonic-nav ul.nav-menu, .themonic-nav div.nav-menu > ul {
　　　border-bottom-color: #6AA121};

But when i added it to the css it didnt work but when i added it to the themes custom css section it worked..

But here is the very confusing part… after i had all the tabs and the line underneath the way i wanted i tried to add another code to change something else and it reverted all the changes. Even when i removed the code i had added the tabs wont go back to the colour i had them!

Very frustrating i have to say so can anyone tell me why this is happening?