External link decorations are already enabled in the documentation
content, but the RTD theme doesn't extend this to the sidebar. This
copies the css from the RTD theme and adds it to the sidebar.
This makes it less of a surprise when you click on a link and find
yourself on a completely different website.
The contentui sets the page with to be infinite in order to add a second column.
We do not use this feature, so we set the width back to normal. Also make sure our theme_overrides are last in conf.py to make sure they override the contentui css.
David Lechner
Laurens Valk