The shopping cart (shopping_cart.php) buttons to update the quantity or delete item were constantly flowing under to the next line whenever the screen size was reduced. Especially on mobile devices. From a visual aspect it drove me crazy. So I believe I found the solution to lock them together using the user.css file (/templates/override/static/user.css).
Simply add
to the css file which overrides the default input-group and locks the qty, update and remove fields together.
The !important property doesn't seem to be required so don't add it unless needed. My understanding is that you don't use that property unless the override isn't affected. This might impact another area that uses the .input-group but I didn't find any after a quick search.
Hope this helps you if needed/wanted.
-Cary