if a picture paints a thousand words...

But if not login to a jenkins instance like ci.jenkins.io or weekly.ci.jenkins.io and go to your configure page.

e.g. https://weekly.ci.jenkins.io/me/configure

scroll to notification URL

Change is to Jenkins classic

Save the page.

go to the confiugre page again

expected results

the dropdown text is rendered correctly with an isolated downward chevron thingy to trigger the dropdown.

actual results

see screenshot above  the dropdown box is too narrow and the chevron is rendered over the text.

notes

it is a regression against some previous jenkins version...