What did I type to cause gray background in question?

Question

Sometimes I'll be navigating within a question, probably typing a comment, the question will get highlighted with a gray background, like this:

I guess I must have typed a keyboard shortcut, but I don't know what it is. What does this shading mean, and what did I type to cause it?

The only way I've found to undo it is to reload the page.

Answer 1

You probably hit j or k, which are the keyboard shortcuts for navigating up and down by post. If you go to a post with many answers, and tap j several times in a row, you'll navigate through the answers down the page.

The currently selected post is highlighted in grey shadow.