The list of standard selects cannot be affected, since It is rendered not by the browser, but by the operating system. But you can use js-plugin for select, for example, select2 . In it you can, among other things, stylize a scrollbar.
For example:
.select2-container--default .select2-results > .select2-results__options::-webkit-scrollbar { height: 10px; width: 10px; } .select2-container--default .select2-results > .select2-results__options::-webkit-scrollbar-thumb { background-clip: padding-box; background-color: rgba(50, 50, 50, 0.25); border-radius: 10px; border: 2px solid transparent; } .select2-container--default .select2-results > .select2-results__options::-webkit-scrollbar-thumb:hover { background-color: rgba(50, 50, 50, 0.5); }