Customize layout of textarea scrollbar — radicle-desktop

Currently the overlayscrollbars package we use has no support for textareas https://github.com/KingSora/OverlayScrollbars/discussions/504

Once this lands we probably can revert this change and use overlayscrollbars as in the other places.

This change only changes the design of the scrollbar to not be bright white in dark mode, it does not hide the scrollbar after x amount of time.

     color: var(--color-foreground-dim);
   }
   textarea::-webkit-scrollbar {
     width: 7px;
     height: 7px;
   }
   textarea::-webkit-scrollbar-track {
     background-color: transparent;
   }
   textarea::-webkit-scrollbar-thumb {
     background-color: var(--color-fill-ghost);
     border-radius: 4px;
   }
   .dragover {
     position: absolute;
     opacity: 0.5;