Menu button on responsive theme: change the colour

up! I miss one strategic word!

I’d like to change the colour of the Menu button in a twenty twelve child menu, as it is seen in the responsive way on a mobile.

But, of course I’d not like to lose the code when I upgrade the child theme. Can you please tell me how to do it?

Looking at the style.css file I saw this

.menu-toggle, input[type="submit"], input[type="button"], input[type="reset"], article.post-password-required input[type="submit"], .bypostauthor cite span {
  background-color: #080882;
  background-image: -moz-linear-gradient(center top , #080882, #080882);
  background-repeat: repeat-x;
  border: medium none;
  border-radius: 3px;
  box-shadow: 0 1px 2px rgba(64, 64, 64, 0.1);
  color: #fff;
  font-size: 0.785714rem;
  font-weight: normal;
  line-height: 1.42857;
  padding: 0.428571rem 0.714286rem;

Can you please give me an advise which is the code to have the buttons coloured #080882 on the mobile devices?