Hello,
We don’t have such option in our theme. You may try to add the below code to Theme Options > Custom CSS to hide sizes by default and display on hover only
.content-product .product-details .st-swatch-in-loop {
-webkit-transition: all 0.2s ease-in-out;
transition: all 0.2s ease-in-out;
opacity: 0;
}
.content-product:hover .product-details .st-swatch-in-loop {
opacity: 1;
}
Also, you can submit a feature request here https://www.8theme.com/taskboard/ if you want to get any new options and our developers will check that.
Regards