en.javascript.info/2-ui/2-events/01-introduction-browser-events/06-hide-message/solution.md

To add the button we can use either position:absolute (and make the pane position:relative) or float:right. The float:right has the benefit that the button never overlaps the text, but position:absolute gives more freedom. So the choice is yours.

Then for each pane the code can be like:

pane.insertAdjacentHTML("afterbegin", '<button class="remove-button">[x]</button>');

Then the <button> becomes pane.firstChild, so we can add a handler to it like this:

pane.firstChild.onclick = () => pane.remove();