whenever the css for code coverage changes then the browser still has cache for the old file
A very easy way would be to include the version number in the URL of the css

So change:
<link href="https://github.com/%7B%7Bpath_to_root%7D%7D_css/bootstrap.min.css" rel="stylesheet" type="text/css">
to
<link href="https://github.com/%7B%7Bpath_to_root%7D%7D_css/bootstrap.min.css?v={{version}}" rel="stylesheet" type="text/css">

that should be done for all the css files