gravityforms

Hi,
Hope I can find someone willing to giving me a hand with something that must be really simple for you, but me.

Here's the problem:

I have a radio buttons form and instead of radio I want to use customised buttons. As the form must be responsive, I would like to use max width in order to reduce or expand automatically the width. Here's the code that I am using:

#field_2_23 ul.gfield_radio li input[type="radio"] + label {
border: 1px solid #d1d1d1;
color: #808080;
background-color: #ffffff;
width: 134px !important;
height: 50px;
border-radius: 5px;