Hi there,

You can do that by adding this CSS at your Custom CSS area:

.laborator-woocommerce .product-single .entry-summary .variations_form .variations .value {
    width: 207px;
    float: left;
}

Anyway, its not recommended to limit the size of the selector as it can change on different screen views.

Hi seduco1,

It's the same, the reason why I said it's not recommended is because setting an exact width to any button is not a good idea, it can work great but it also can show more longer or shorter on some screens. 

Couldn't understand what you said. You have the look as you wanted firstly, and I checked it on mobile too it looks good.

If you're looking for professional help in this matter, there's always someone available for such tasks on the Envato Studio or WP Kraken. Pricing and timeline are always straightforward there and that's the main reason for recommending those services.