It is impossible to style radio button directly (at least in this context where you want to change the dot).
Instead you replace the "real" control with span that looks like the control you want to replace (in this case radio button) and hide the real one. The look of the dot is usually controlled by an image in the relevant color.
You have to handle the events such as click and reflect the event back to the real control.
Good example of such change is here
Custom check and radio boxes[
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