This is an css question, so really this is not the right place for it.
However, you need to use the + operator and the :checked selector like this:
(This assumes your radio buttons are built like this):
<input type="radio" id="my_awesome_radio_1" value="value1" />
<label for="my_awesome_radio_1">Value 1</label>
<input type="radio" id="my_awesome_radio_2" value="value2" />
<label for="my_awesome_radio_2">Value 2</label>
<input type="radio" id="my_awesome_radio_3" value="value3" />
<label for="my_awesome_radio_3">Value 3</label>
CSS-Code:
input[type=radio] {
display:none;
}
input[type=radio] + label {
display: inline-block;
border: 1px solid #eee;
padding: 10px;
margin-right: 10px;
color: #eee;
}
input[type=radio]:checked + label {
background: #eee;
color: #000;
}