You’re right, to me it looks like it should be working how you would like it to be working. So I took a look at what the MDN (bookmark this, it’s an essential reference for web dev) select page said to see if it said anything that could help. I found this:
Styling with CSS
The <select> element is notoriously difficult to style productively with CSS. You can affect certain aspects like any element — for example, manipulating the box model, the displayed font, etc., and you can use the appearance property to remove the default system appearance .
For more useful information on styling <select> , see: