Hide amount selection drop-down menu
First, ensure that the default amount is specified under Products -> PW Gift Card -> Default so that it is automatically selected when the customer arrives on the gift card product.
Then you can hide the Select Amount dropdown menu by taking the following steps:
1. Log into your WordPress Admin area.
2. Click on Appearance -> Customize -> Additional CSS (note: not every theme has this setting, though most do.)
3. Paste the following CSS into the field and save:
.product-type-pw-gift-card .variations { display: none !important; }