Pure Vanilla CSS / HTML solution in 2021. It uses the CSS appearance: none;
property.
Seems to be compatible with all major browsers at this time:
https://caniuse.com/?search=appearance%3A%20none
input[type="radio"]{
appearance: none;
border: 1px solid #d3d3d3;
width: 30px;
height: 30px;
content: none;
outline: none;
margin: 0;
box-shadow: rgba(0, 0, 0, 0.24) 0px 3px 8px;
}
input[type="radio"]:checked {
appearance: none;
outline: none;
padding: 0;
content: none;
border: none;
}
input[type="radio"]:checked::before{
position: absolute;
color: green !important;
content: "\00A0\2713\00A0" !important;
border: 1px solid #d3d3d3;
font-weight: bolder;
font-size: 21px;
}
_x000D_
<input type="radio" name="radio" checked>
<input type="radio" name="radio">
<input type="radio" name="radio">
_x000D_