Please add follwoing css your assets/component-cart.css at bottom of the file .
.cart__dynamic-checkout-buttons div[role=button] {border-radius: 10px!important;}
iframe._1qHzu06EhANVVG3mlfU6Ho.paypalLight._9ATKCDN1-_J5vniMChq1n {border-radius: 10px;}
Thanks!