examples: Fix checkout page (#29886)

Author: MartijnCuppens

site/content/docs/4.3/examples/checkout/index.html

@@ -122,7 +122,7 @@ <h4 class="mb-3">Billing address</h4>
         <div class="row">
           <div class="col-md-5 mb-3">
             <label for="country">Country</label>
-            <select class="custom-select d-block w-100" id="country" required>
+            <select class="form-select" id="country" required>
               <option value="">Choose...</option>
               <option>United States</option>
             </select>
@@ -132,7 +132,7 @@ <h4 class="mb-3">Billing address</h4>
           </div>
           <div class="col-md-4 mb-3">
             <label for="state">State</label>
-            <select class="custom-select d-block w-100" id="state" required>
+            <select class="form-select" id="state" required>
               <option value="">Choose...</option>
               <option>California</option>
             </select>
@@ -149,30 +149,30 @@ <h4 class="mb-3">Billing address</h4>
           </div>
         </div>
         <hr class="mb-4">
-        <div class="custom-control custom-checkbox">
-          <input type="checkbox" class="custom-control-input" id="same-address">
-          <label class="custom-control-label" for="same-address">Shipping address is the same as my billing address</label>
+        <div class="form-check">
+          <input type="checkbox" class="form-check-input" id="same-address">
+          <label class="form-check-label" for="same-address">Shipping address is the same as my billing address</label>
         </div>
-        <div class="custom-control custom-checkbox">
-          <input type="checkbox" class="custom-control-input" id="save-info">
-          <label class="custom-control-label" for="save-info">Save this information for next time</label>
+        <div class="form-check">
+          <input type="checkbox" class="form-check-input" id="save-info">
+          <label class="form-check-label" for="save-info">Save this information for next time</label>
         </div>
         <hr class="mb-4">
 
         <h4 class="mb-3">Payment</h4>
 
         <div class="d-block my-3">
-          <div class="custom-control custom-radio">
-            <input id="credit" name="paymentMethod" type="radio" class="custom-control-input" checked required>
-            <label class="custom-control-label" for="credit">Credit card</label>
+          <div class="form-check">
+            <input id="credit" name="paymentMethod" type="radio" class="form-check-input" checked required>
+            <label class="form-check-label" for="credit">Credit card</label>
           </div>
-          <div class="custom-control custom-radio">
-            <input id="debit" name="paymentMethod" type="radio" class="custom-control-input" required>
-            <label class="custom-control-label" for="debit">Debit card</label>
+          <div class="form-check">
+            <input id="debit" name="paymentMethod" type="radio" class="form-check-input" required>
+            <label class="form-check-label" for="debit">Debit card</label>
           </div>
-          <div class="custom-control custom-radio">
-            <input id="paypal" name="paymentMethod" type="radio" class="custom-control-input" required>
-            <label class="custom-control-label" for="paypal">PayPal</label>
+          <div class="form-check">
+            <input id="paypal" name="paymentMethod" type="radio" class="form-check-input" required>
+            <label class="form-check-label" for="paypal">PayPal</label>
           </div>
         </div>
         <div class="row">