Reply To: where change product size attribute radio button checked size ?

Hello,

I saw the screenshot you attached.

Sorry, but it is not possible to make the design the same as you mentioned in the image of your reply.

Therefore to add a border around the variations try adding the following Custom CSS in the Global Custom CSS area under Theme Settings >> Custom CSS.

.woodmart-swatch.swatch-on-single {
    border: 1px solid blue;
    padding: 10px;
}

Best Regards.