Dropdown should automatically change value on arrow up/down

The native <select> element has the behavior that, on focus, pressing arrow up/down instantly changes the value. See https://developer.mozilla.org/docs/Web/HTML/Reference/Elements/select (tested on Chrome and Firefox)

However, with Radix UI, it just opens the dropdown back up (and sometimes doesn't select the currently selected item). For example, in https://diffs.com/#themes I should be able to select one option then just press the down arrow to scroll between the themes, but instead it takes multiple clicks/keypresses to switch theme.