Custom styling TB-Megamenu
TB Mega Menu module has a CSS folder. Use that as your reference. It also has a styles sub-folder that IMO would be of greatest benefit. Just copy one of the whole styles/*.css files over and adapt it. No need to hunt it down.

To target a menu on a specific page you will need to inject a CSS class into that page via a preprocess_page hook or Context or some other preferred method. You need to set it closer to root level (ie html or body tag) than that of .tb-megamenu class occurence in the html. Having done that all you need do is prepend your injected class to every single selector that you use, as in:

.tb-megamenu.style-black .nav &gt; li &gt; a:focus,
.tb-megamenu.style-black .nav &gt; li &gt; a:hover {
  background-color: #222;
  color: #7bb9e0;
}


becomes:

.my-page-class .tb-megamenu.style-black .nav &gt; li &gt; a:focus,
.my-page-class .tb-megamenu.style-black .nav &gt; li &gt; a:hover {
  background-color: #222;
  color: #7bb9e0;
}