I'm afraid that customizations such as this are not covered under our support policy, so implementing this or modifying it isn't something we can assist with.
If you need help implementing this or modifying it further, my recommendation is reaching out to a developer who is experienced in customizing WordPress & WooCommerce.
FYI, the following styles have been used to style HTML select fields.
-o-transition: all 0.3s;
-webkit-transition: all 0.3s;
border: 2px solid #e5e5e5;
padding: 0 16px;
transition: all 0.3s;