Grouped products

On my webshop www.t-supporting.nl i add different product.
I made grouped product because of the different sizes of each products we have in de shop.

But the buttons of the grouped product are very big (see attached picture "RED area").
Is it possible to make this buttons smaller??

Or is there an another way to make this grouped products looked nicer than it is now.

 

Hello,

Paste this code in Custom CSS
Appearance > Theme Option > Styling Option > Custom CSS

Code:

.sidebar.becomemember input[type="button"].minus {
width: 25px;
height: 25px;
}
.sidebar.becomemember .input-text.qty {
width: 45px;
height: 25px;
}
.sidebar.becomemember input[type="button"].plus {
width: 25px;
height: 25px;
}