Simplewaita/source/common/paned.scss

paned {
  > separator {
    min-width: 2*$border_width;
    min-height: 2*$border_width;
    -gtk-icon-source: none; // defeats the ugly default handle decoration. 
    border-width: $border_width; //for some reason, it's drawn twice as wide (only in GTK3!)
    border-style: solid;
    background-image: radial-gradient(circle closest-side, $fg_color 0%, $fg_color 75%, transparentize($fg_color, 1) 100%);
    background-clip: padding-box;
    //background-size:  2*$border_width + 2px  2*$border_width + 2px;
    background-repeat: no-repeat;
    background-position: center;
    
    @include relief($bg_color);

    &:selected { @include relief($selected_bg_color); } // FIXME is this needed?

    &.wide {
      min-width: 5px;
      min-height: 5px;
      
    }
  }

  &.horizontal > separator {
    //background-repeat: repeat-y;

    &:dir(ltr) {
      //margin: 0 -8px 0 0;
      //padding: 0 8px 0 0;
      //background-position: left;
    }
    &:dir(rtl) {
      //margin: 0 0 0 -8px;
      //padding: 0 0 0 8px;
      //background-position: right;
    }

    &.wide {
      margin: 0;
      padding: 0;
      //background-repeat: repeat-y, repeat-y;
      //background-position: left, right;
    }
  }

  &.vertical > separator {
    //margin: 0 0 -8px 0;
    //padding: 0 0 8px 0;
    //background-repeat: repeat-x;
    //background-position: top;

    &.wide {
      margin: 0;
      padding: 0;
      //background-repeat: repeat-x, repeat-x;
      //background-position: bottom, top;
    }
  }
}