when I make a number input field like this:
Then the number field gets a spinner added to it whenever I hov
It is not possible to do this with the Browser specific style. You would need to either build that functionality yourself using some Javascript or look for a premade script on the interwebs.
You can only hide those Shadow DOM elements as they trigger very browserspecific css-attributes to provide the functionalitys like onclick or onhover.
See: http://css-infos.net/property/-webkit-appearance (You could trigger another behaviour for your Input-Field, but you cant force it to be always visible)