Unable to change scrollbar size no matter what I try

I’ve looked at all the threads about scrollbars on this forum. I’ve tried many different snippets in my styles.less file but none of them do anything.

What am I missing here?

This my current styles.less which doesn’t increase scrollbar size:

.scrollbars-visible-always {
  ::-webkit-scrollbar {
    width: 20px;
    height: 20px;
    &-track {
        border: 0px;
        border-radius: 0px;
        background-color: #444 !important;
    &-thumb {
        background-color: rgba(255,200,200,0.35) !important;
        border: 0px;
        border-radius: 9px;

Operating System: Manjaro Linux
KDE Plasma Version: 5.20.2
KDE Frameworks Version: 5.75.0
Qt Version: 5.15.1
Kernel Version: 5.8.18-1-MANJARO
OS Type: 64-bit
Processors: 16 × AMD Ryzen 7 2700X Eight-Core Processor
Memory: 15.6 GiB of RAM
Graphics Processor: Radeon RX 580 Series