docs: fix scrollbar issues in both sidebars
docs: fix scrollbar issues in both sidebars

- theme issue workaround: set width of scrollbar content, so that the
  scrollbar doesn't shrink the available space once it appears
- theme issue workaround: add padding-right to TOC content, so that the
  text doesn't touch the scrollbar
- make TOC scrollbar transparent while not hovering it, as it's
  distracting otherwise on large TOC lists

bastimeyer/streamlink,melmorabity/streamlink,chhe/streamlink,bastimeyer/streamlink,chhe/streamlink,streamlink/streamlink,gravyboat/streamlink,gravyboat/streamlink,melmorabity/streamlink,streamlink/streamlink