Could you kindly specify which price you want to increase: in a grid on the product page and in the top under the title or price that is shown after selection: https://gyazo.com/175a13f78ce5f93501668f5203a15f0a
If you mean this price, add this code:
.woocommerce-variation-price ins .amount {
font-size: 30px;
}
.
