I follow what Mat said and hide the original styling. Here's an example with green coloring that you can play around with...
input[type="radio"],
.tc-tiddler-body input[type="radio"],
.tc-tiddler-preview-preview input[type="radio"],
.tc-sidebar-scrollable input[type="radio"] {
-webkit-appearance: none;
background: none;
box-shadow: none;
height: 0;
margin: 0 0 0 1em;
padding: 0;
position: relative;
width: 0;
}
input[type="radio"]::before,
.tc-tiddler-body input[type="radio"]::before,
.tc-tiddler-preview-preview input[type="radio"]::before,
.tc-sidebar-scrollable input[type="radio"]::before {
background-color: rgba(var(--primary),0.2);
border: none;
border-radius: 1em;
box-shadow:
0 3px 0 -1px rgba(0,255,0,0.4),
0 0 0 1px rgb(0,255,0,0.45) inset,
0 -2px 0 -1px rgb(0,255,0,1) inset;
content: " ";
display: inline-block;
height: 0.75em;
left: -1em;
position: absolute;
top: -0.75em;
width: 0.75em;
}
input[type="radio"]:checked::before,
.tc-tiddler-body input[type="radio"]:checked::before,
.tc-tiddler-preview-preview input[type="radio"]:checked::before,
.tc-sidebar-scrollable input[type="radio"]:checked::before {
background-color: rgba(0,255,0,1);
border: none;
border-radius: 1em;
box-shadow:
0 3px 0 -1px rgba(0,255,0,0.4),
0 0 0 1px rgb(0,255,0,0.45) inset,
0 -2px 0 -1px rgb(0,255,0) inset;
content: " ";
display: inline-block;
height: 0.75em;
left: -1em;
position: absolute;
top: -0.75em;
width: 0.75em;
}