Change size quantity box product

Using Opencart 1.5.6. I would like to change the width of the quantity box on the product page. Any idea where I can find this?

get the selector of quantity box then use css

for examle
if the selector is .box use

.box{
width:50px;
}

I know what to do with css, but I can not find it on the stylesheet.
What do you mean with 'selector'?

in browser just right click on the box u want to resize then click on inspect element ..

under the window click on the + sign to get its unique selector(something like 'div.span.div.u.li.div' nested selector) and give it display none... then simply copy and paste it on your main css or custom css ... simple

Hi thanks for the respons. I should have known this, but was working in Safari. But now the weird thing is happening. In Firefox and Chrome the quantity box is adjusting to the number inserted. It is Safari which is causing the problem. If you have for instance 100 products, the width of the box is too small and not adjusting. Any idea how to fix this, is an Opencart problem as it seems.

Can somebody help me with this issue? In Safari the quantity box is too small for more than two digits. Why is it working in Firefox etc. but not in Safari?????