Websites can have expandable/collapsible sections; that allows users to focus or unfocus on regions. Like Twitter Bootstrap has accordion. For example, see the far left region of this site -
https://github.com/facebook/react/tree/main/packages
What is the keyboard command to toggle (expandable/collapsible) the state of sections (on the far left in the example site); all at the same time. I know it exist as I used it before. I just cannot recall it.
NOTE - This is NOT a feature specific to github. I mentioned it to give an example. It is a feature all websites with collapsible sections should support. If this is new to you, please do not thumb down but step aside and make way for someone who knows more to address the question.