Here’s a video of trying to collapse a cell.
Windows 10. Chrome 64.
Sure! The caret button toggles whether a section is pinned or not - whether it stays open all the time. To toggle it, you can click the gray background or the cell name in the left-hand side (though it looks like your screen is <1000px wide, so that cell name is cropped out)
Got it. Thanks! I’m used to the pushpin icon for “always open” and the down/up arrow for opening/collapsing.