WhiteSur-gtk-theme/src/sass/gnome-shell/common/_overview.scss

.overview-controls {
  padding-bottom: 32px;
}

%overview_scrollbar {
  StBin#trough {
    background-color: $light_divider_color;
  }

  StButton#vhandle, StButton#hhandle {
    background-color: $light_hint_fg_color;
    &:hover { background-color: $light_alt_fg_color; }
    &:active { background-color: $light_fg_color; }
  }
}

#overview {
  StScrollBar { @extend %overview_scrollbar; }
}