REQUEST: custom CSS Box

[MG-Sky]

It would be nice to have a box where i could override some css elements like:

1. original:
   @media(max-width: 500px) {
   .sites {
   -ms-overflow-style:none;
   margin-top: 20px;
   max-height: calc(100% - 65px);
   scrollbar-width: none;
   width: 100%
   }

2. custom:
   @media(max-width: 300px) {
   .sites {
   -ms-overflow-style:none;
   margin-top: 20px;
   max-height: calc(100% - 65px);
   scrollbar-width: none;
   width: 100%
   }

right now all changes are discarded once docker is restarted.
smth like that one: https://github.com/pawelmalak/flame/wiki/Custom-CSS