Which page is this menu in? I didn't meet a menu looks like the screenshot...
Could you please give me a link?
It's on product pages where users would choose the quantity they choose to buy.
Is that on hover?
Yes, the appearance of the menu is the OS native appearance. Your screenshot should be a customized appearance.
I don't know why I can only see the native appearance.
Hmm, I'm seeing it on chrome.
Prateek changed the appearance today because of this: https://phabricator.wikimedia.org/T96695