Feeling that handsome’s built-in left sidebar display method is not suitable, so I modified it by referring to the tutorial Optimizing Sidebar Display: Achieving More Beautiful Classification Display by UCW.
Suggest import Font Awesome library before start, you can add codes below to Theme settings -> developer settings -> custom output HTML
<head> code .
<link rel="stylesheet" href="https://firstname.lastname@example.org/css/font-awesome.min.css">
libs/Content.php and insert codes at the location shown by the blue line: