fix: bg to quiqqer-coupons-couponcodeinput

bin/frontend/controls/CouponCodeInput.css

@@ -7,6 +7,7 @@ div + .quiqqer-coupons-field {
 }
 
 .quiqqer-coupons-couponcodeinput {
+    background: rgba(0, 0, 0, 0.05);
     display: flex;
     padding: 5px;
 }