TOC runs off the page for long documents

[d0ugal]

Originally reported against MkDocs. mkdocs/mkdocs#204

[Mailaender]

This seems to be a regression, because mkdocs==0.17.3 example: https://docs.openra.net/en/release/traits/ will show scrollbars.

[Mailaender]

.bs-sidebar {
    max-height: 640px; max-width: 240px; overflow: auto;
}

.nav-link {
    overflow-wrap: anywhere;
}

is my extra CSS solution for mkdocs==1.4.1 which adds the scrollbar back in and avoids long class names overflowing: https://docs.openra.net/en/bleed/traits/