<head>
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/4.7.0/css/font-awesome.min.css">
</head>
<h2>Responsive Checkout Form Using CSS</h2>
<p>Resize the browser window to see the effect. When the screen is less than 800px wide, make the two columns stack on top of each other instead of next to each other.</p>
<div class="row">
  <div class="col-75">
    <div class="container">
      <form action="/action_page.php">
      
        <div class="row">
          <div class="col-50">
            <h3>Billing Address</h3>
            <label for="fname"><i class="fa fa-user"></i> Full Name</label>
            <input type="text" id="fname" name="firstname" placeholder="Your Name ">
            <label for="email"><i class="fa fa-envelope"></i> Email</label>
            <input type="text" id="email" name="email" placeholder="youremail@example.com">
            <label for="adr"><i class="fa fa-address-card-o"></i> Address</label>
            <input type="text" id="adr" name="address" placeholder="your address">
            <label for="city"><i class="fa fa-institution"></i> City</label>
            <input type="text" id="city" name="city" placeholder="your city">

            <div class="row">
              <div class="col-50">
                <label for="state">State</label>
                <input type="text" id="state" name="state" placeholder="your state">
              </div>
              <div class="col-50">
                <label for="zip">Zip</label>
                <input type="text" id="zip" name="zip" placeholder="your zipcode">
              </div>
            </div>
          </div>

          <div class="col-50">
            <h3>Payment</h3>
            <label for="fname">Accepted Cards</label>
            <div class="icon-container">
              <i class="fa fa-cc-visa" style="color:navy;"></i>
              <i class="fa fa-cc-amex" style="color:blue;"></i>
              <i class="fa fa-cc-mastercard" style="color:red;"></i>
              <i class="fa fa-cc-discover" style="color:orange;"></i>
            </div>
            <label for="cname">Name on Card</label>
            <input type="text" id="cname" name="cardname" placeholder="John">
            <label for="ccnum">Credit card number</label>
            <input type="text" id="ccnum" name="cardnumber" placeholder="1111-2222-3333-4444">
            <label for="expmonth">Exp Month</label>
            <input type="text" id="expmonth" name="expmonth" placeholder="August">
            <div class="row">
              <div class="col-50">
                <label for="expyear">Exp Year</label>
                <input type="text" id="expyear" name="expyear" placeholder="2021">
              </div>
              <div class="col-50">
                <label for="cvv">CVV</label>
                <input type="text" id="cvv" name="cvv" placeholder="352">
              </div>
            </div>
          </div>
          
        </div>
        <label>
          <input type="checkbox" checked="checked" name="sameadr"> Shipping address same as billing
        </label>
        <input type="submit" value="Continue to checkout" class="btn">
      </form>
    </div>
  </div>
  <div class="col-25">
    <div class="container">
      <h4>Cart <span class="price" style="color:black"><i class="fa fa-shopping-cart"></i> <b>4</b></span></h4>
      <p><a href="#">Product 1</a> <span class="price">$15</span></p>
      <p><a href="#">Product 2</a> <span class="price">$5</span></p>
      <p><a href="#">Product 3</a> <span class="price">$8</span></p>
      <p><a href="#">Product 4</a> <span class="price">$2</span></p>
      <hr>
      <p>Total <span class="price" style="color:black"><b>$30</b></span></p>
    </div>
  </div>
</div>
body {
  font-family: Arial;
  font-size: 17px;
  padding: 8px;
}

* {
  box-sizing: border-box;
}

.row {
  display: -ms-flexbox; /* IE10 */
  display: flex;
  -ms-flex-wrap: wrap; /* IE10 */
  flex-wrap: wrap;
  margin: 0 -16px;
}

.col-25 {
  -ms-flex: 25%; /* IE10 */
  flex: 25%;
}

.col-50 {
  -ms-flex: 50%; /* IE10 */
  flex: 50%;
}

.col-75 {
  -ms-flex: 75%; /* IE10 */
  flex: 75%;
}

.col-25,
.col-50,
.col-75 {
  padding: 0 16px;
}

.container {
  background-color: #f2f2f2;
  padding: 5px 20px 15px 20px;
  border: 1px solid lightgrey;
  border-radius: 3px;
}

input[type=text] {
  width: 100%;
  margin-bottom: 20px;
  padding: 12px;
  border: 1px solid #ccc;
  border-radius: 3px;
}

label {
  margin-bottom: 10px;
  display: block;
}

.icon-container {
  margin-bottom: 20px;
  padding: 7px 0;
  font-size: 24px;
}

.btn {
  background-color: #04AA6D;
  color: white;
  padding: 12px;
  margin: 10px 0;
  border: none;
  width: 100%;
  border-radius: 3px;
  cursor: pointer;
  font-size: 17px;
}

.btn:hover {
  background-color: #45a049;
}

a {
  color: #2196F3;
}

hr {
  border: 1px solid lightgrey;
}

span.price {
  float: right;
  color: grey;
}

/* Responsive layout - when the screen is less than 800px wide, make the two columns stack on top of each other instead of next to each other (also change the direction - make the "cart" column go on top) */
@media (max-width: 800px) {
  .row {
    flex-direction: column-reverse;
  }
  .col-25 {
    margin-bottom: 20px;
  }
}

External CSS

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External JavaScript

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