How to…

How to disable the background shadow

theme.css.liquid:

.header-wrapper--overlay{
  position:absolute;
  top:0;
  left:0;
  right:0;
  z-index:6;
  background:none;
  
  /* Disable background gradient
  background:linear-gradient(180deg, rgba(0, 0, 0, 0.3) 0%,transparent)
  */
}

Rounded buttons

Rounded corners for buttons See: https://community.shopify.com/c/shopify-design/rounding-corners-of-all-buttons/td-p/649391/page/2

.btn, 
.btn--secondary,
.shopify-payment-button, 
.shopify-payment-button .shopify-payment-button__button--unbranded {
    border-radius: 30px !important;
    outline: none !important;
}