How do I contain feed items and keep them from overflowing into the next column using CSS?

Answer 1

Without the specifics (like a screenshot) I can't be 100% sure but I suspect you want to use the "overflow" CSS property (see: https://developer.mozilla.org/en-US/docs/Web/CSS/overflow).

There is an interactive example there but it's likely you will want to try "hidden" (don't show anything), "scroll" (show scrollbars all the time) or "auto" (show scroll bars only if the content is too big).

If you want to customize the horizontal or vertical overflow behavior separately (for example only scroll horizontally, not vertically) you can. use "overflow-x" and "overflow-y", documentation for both are linked from the above page.