Hello,

Please add this code to the Theme Settings > Custom CSS > Global:

body .woocommerce-product-gallery .product-labels .onsale {
background-color: red;
color:yellow;
}

As for the menu, You can change the font by means of the Advanced typography option, which allows you to choose the item from a drop-down or insert your custom CSS class. Please navigate to the Theme Settings > Typography > Advanced Typography.

Here is the documentation providing more detailed instructions: https://xtemos.com/docs/woodmart/advanced-typography-settings/

Best Regards