@waylan last updated the RTD theme from upstream 0.4.1 in 2018 with #1594. Upstream is now at 0.5.2 and I think it's time to bring MkDocs' copy on-par.

While I could just copy the version into a PR I was wondering if there will be dragons lurking with such an approach. So, maybe someone a bit more familiar with this project could provide insights as for how to properly test such a change.

Btw, what prompted me to look into this was the improved styling of the navigation captions.

I could fix this in my site by adding a few lines to my extra.css but I thought updating the theme would be a bit more "sustainable".

.wy-menu-vertical header,
.wy-menu-vertical p.caption {
  color: #55a5d9;
  font-size: 85%;
  margin: 12px 0 0;
}