Compared to v4, v5's docs have a fixed-width, center aligned container. I wanted to keep that look of a centered container, but add a third column to our docs for fitting in a sidebar table of contents. Lately, the ToC has been wildly unhelpful as the constant scrolling up and down to find a link isn't saving me anytime.
Getting that third column though means either sacrificing significant width from the content column, going fullscreen again (don't want to do), or adding a wider container. I chose the last option and rather than write CSS that limits an even wider container to just our docs, I'm adding it to the core.
Let the feedback rip!
Preview: https://deploy-preview-30354--twbs-bootstrap.netlify.com/