body {
  overflow-y: scroll;
  ::-webkit-scrollbar {
    width: 10px;
  }
  ::-webkit-scrollbar-thumb {
    background-color: var(--scroll-thumb-color);
    border-radius: 5px;
  }
  ::-webkit-scrollbar-track {
    background-color: var(--scroll-back-color);
    width: 5px;
  }
}

The styles placed at the body, as above, has no effect on the top level scrollbar.

How to fix it?