prevent front end theme from injecting css into wp-admin

Restructure your CSS files and remove !important rules from your .css files and use proper markup (classes, IDs and etc.).

e.g.

a, .entry-summary a, .entry-content a {
  color: #06F !important;
  font-weight: 400;
}

Judging from the test WS which was found with site: search in Google using the URL in your Facebook profile (Temper Temper).

Edit 1: Although !important rules can be handy from time to time, usually they broke the structure especially if they are not used with proper and detailed planning.