Increasing Scrollbar width does not increase Hitbox of the increment and decrement buttons

Hello Stackoverflow community! I have this scrollable combobox in my javafx desktop application that I want to be wider as the default is very narrow.

I increase the width by setting:

.scroll-bar > .increment-button, 
.scroll-bar > .decrement-button {
    -fx-padding: 10.0px;
}

in my css file.

While that widens the scrollbar and its buttons visually the hitboxes actually stay the same size, so if I click like this the combobox popup collapses:

I could not find anyone with a similar issue, which I find weird as this would seem like a very basic issue, unless nobody ever widens scrollbars. So its probably some super obvious little thing that I am doing wrong and everyone else is not ^^.