Improve experience on small screens

These patches improve the experience on mobile devices, the patch is not perfect, but at least it improves compared to the current situation on mobile devices for some of the most common pages like hompage and edit bug (bug details).

Before: After:

However I am not a native web developer nor familiar with the workflow of submitting patches for our Bugzilla. What would be the best practice to keep it updateable without to many merge conflicts?