Quantity +/- Buttons Odd On Iphone

So I've played around with making the quantity field a little larger (would like it to support 4-5 characters) but on my iPhone it looks all wonky (see attached). It happens in Safari and Chrome. Doesn't matter if in portrait or landscape mode. The funny thing is on any mobile phone emulators it looks just fine so not sure how to track down what is causing the issue or how to fix it. Example product: https://fastdecals.com/shop/mix-bag/square-decal-sticker.html