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HTML 

              
                <div>&nbsp;</div>
<div class="app-container">
  <div class="cart">
    <div class="cart-control-bar">
      <span class="cart-control-bar-title">Checkout</span>
    </div>
    <div class="cart-body">
      <div class="cart-step cart-step-0">
        <h2 class="cart-fieldset-header">Donate</h2>
        
        <div class="cart-controls">
          <label class="cart-label">Fund</label>
          <select class="cart-select cart-width-1-1">
            <option>Area of greatest needs</option>
            <option>If there was a need</option>
            <option>For multiple funds</option>
          </select>
        </div>
        <div class="cart-controls is-required">
          <label class="cart-label">Amount</label>
          <input type="text" class="cart-input cart-width-1-1">
          <p class="cart-input-error-message">Amount is required</p>
        </div>
        <div class="cart-controls">
          <label class="cart-label">
            <input type="checkbox">
            Make this a monthly recurring donation
          </label>
          <a href="#/" class="cart-button cart-button-step cart-button-primary" data-to-cart-step="1">Next &#x279d;</a>
        </div>
      </div> <!-- END step 0 -->
      
      <div class="cart-step cart-step-1">
        <h2 class="cart-fieldset-header">Contact details</h2>
        <form action="">
          <div class="cart-controls">
            <label class="cart-label">First Name</label>
            <input type="text" class="cart-input cart-width-1-1">
          </div>
          <div class="cart-controls">
            <label class="cart-label">Last Name</label>
            <input type="text" class="cart-input cart-width-1-1">
          </div>
          <div class="cart-controls">
            <label class="cart-label">Email Name</label>
            <input type="text" class="cart-input cart-width-1-1">
          </div>
          <div class="cart-controls">
            <label class="cart-label">Phone</label>
            <input type="text" class="cart-input cart-width-1-1">
          </div>
          <a href="#/" class="cart-button cart-button-step cart-button-primary" data-to-cart-step="2">Next &#x279d;</a>
        </form>
      </div> <!-- END step 1 -->
      
      <div class="cart-step cart-step-2">
        <h2 class="cart-fieldset-header">Payment method</h2>
        <div class="cart-method-container">
          <ul class="cart-method-list u-clearfix">
            <li class="cart-method-item">
              <div class="cart-method is-active u-flex-center">
                <svg fill="#3E84E0" height="36" viewBox="0 0 24 24" width="36" xmlns="http://www.w3.org/2000/svg">
                    <path d="M0 0h24v24H0z" fill="none"/>
                    <path d="M20 4H4c-1.11 0-1.99.89-1.99 2L2 18c0 1.11.89 2 2 2h16c1.11 0 2-.89 2-2V6c0-1.11-.89-2-2-2zm0 14H4v-6h16v6zm0-10H4V6h16v2z"/>
                </svg>
              </div>
            </li>
            <li class="cart-method-item">
               <div class="cart-method u-flex-center">
                <img src="https://s27.postimg.cc/54lyg4smb/Pay_Pal.png" height="22">
              </div>
            </li>
            <li class="cart-method-item">
               <div class="cart-method u-flex-center">
                <img src="https://s24.postimg.cc/c12pp1vad/apple_pay.png" height="22">
              </div>
            </li>
          </ul>
        </div>
        
        
        <h2 class="cart-fieldset-header">Payment details</h2>
        <div class="cart-controls">
          <label class="cart-label">Card number</label>
          <input type="text" class="cart-input cart-width-1-1">
        </div>
        <div class="cart-controls">
          <label class="cart-label">Name on card</label>
          <input type="text" class="cart-input cart-width-1-1">
        </div>
        <div class="cart-grid">
          <div class="cart-controls cart-width cart-width-1-2">
            <label class="cart-label">Expiry date</label>
            <input type="text" class="cart-input">
          </div>
          <div class="cart-controls cart-width cart-width-1-2">
            <label class="cart-label">Security code</label>
            <input type="text" class="cart-input">
          </div>
        </div>
        <div class="cart-controls">
          <label class="cart-label">Zip/Postal code</label>
          <input type="text" class="cart-input cart-width-1-1">
        </div>

        <a href="#/" class="cart-button cart-button-step cart-button-primary" data-to-cart-step="3">
          <svg fill="#fff" height="16" viewBox="0 0 24 24" width="16" xmlns="http://www.w3.org/2000/svg">
            <path d="M0 0h24v24H0z" fill="none" class="cart-button-icon"/>
            <path d="M18 8h-1V6c0-2.76-2.24-5-5-5S7 3.24 7 6v2H6c-1.1 0-2 .9-2 2v10c0 1.1.9 2 2 2h12c1.1 0 2-.9 2-2V10c0-1.1-.9-2-2-2zm-6 9c-1.1 0-2-.9-2-2s.9-2 2-2 2 .9 2 2-.9 2-2 2zm3.1-9H8.9V6c0-1.71 1.39-3.1 3.1-3.1 1.71 0 3.1 1.39 3.1 3.1v2z"/>
          </svg>  
          Donate $500
        </a>
      </div> <!-- END step 2 -->
      
      <div class="cart-step cart-step-3 u-text-center">
        <div style="margin:100px 0 150px;">
          <svg fill="#3E84E0" height="96" viewBox="0 0 24 24" width="96" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
            <defs>
              <path d="M0 0h24v24H0V0z" id="a"/>
            </defs>
            <clipPath id="b">
              <use overflow="visible" xlink:href="#a"/>
            </clipPath>
            <path clip-path="url(#b)" d="M14 10H2v2h12v-2zm0-4H2v2h12V6zM2 16h8v-2H2v2zm19.5-4.5L23 13l-6.99 7-4.51-4.5L13 14l3.01 3 5.49-5.5z"/>
          </svg>

          <h2 style="font-weight:400;">Congratulations.<br>Your donation was successful.</h2>
          <p class="subtle">We will send a copy of the receipt to your email.</p>
        </div>
        <a href="#/" class="cart-button cart-button-step" data-to-cart-step="0">
         Return to start
        </a>
      </div> <!-- END step 2 -->
      
    </div>
  </div>
</div>
!

CSS 

              
                html {
  background-color: #eee;
  box-sizing: border-box;
  font-family: 'Roboto', sans-serif;
  font-size: 14px;
  font-weight: 400;
}

*, *:before, *:after {
  box-sizing: inherit;
}

body {
      background-image: url(https://s24.postimg.org/txymqvd9x/child_children_girl_happy.jpg);
    width: 100%;
    height: 100vw;
}

.u-clearfix:before,
.u-clearfix:after {
  content: " ";
  display: table;
}

.u-clearfix:after {
  clear: both;
}

.u-clearfix {
  *zoom: 1;
}

.u-flex-center {
    display: -webkit-flex;
    display: flex;
    -webkit-justify-content: center;
    justify-content: center;
    -webkit-align-items: center;
    align-items: center;
}

.u-text-center {
  text-align: center;
}

.subtle {
  color: #888;
}

input {
  font-family: 'Roboto', sans-serif;
}

.app-container {
  margin: 10vh 5vw;
  width: 380px;
}

.cart {
  background-color: #fff;
  box-shadow: 0 15px 80px 4px rgba(0,0,0,.18);
  width: 100%;
}

.cart-control-bar {
  background-color: #F4F4F4;
  padding: 15px 0;
  text-align: center;
}

.cart-control-bar-title {
  color: #888;
  font-size: 18px;
  font-weight: 400;
}

.cart-body {
  padding: 20px 10px;
}

.cart-step {
  display: none;
}

.cart-step-0 {
  display: block;
}

.cart-fieldset-header {
  color: #888;
  font-size: 12px;
  font-weight: 700;
  letter-spacing: .04em;
  margin-bottom: 15px;
  text-transform: uppercase;
}

.cart-input-error-message {
  color: #F04848;
  max-height: 0;
  font-weight: 500;
  margin: 5px 0 15px;
  overflow: hidden;
  transition: all 600ms ease-out;
}

.cart-controls {
   margin-bottom: 15px;
}

.cart-controls.is-invalid .cart-input-error-message {
  max-height: 100px;
}

.cart-controls.is-invalid .cart-input {
  border: 1px solid #F04848;
}

.cart-controls.is-invalid .cart-input:focus {
  outline: 1px solid #fcd5d5;
}

.cart-label {
  color: #888;
  display: block;
  margin-bottom: 6px;
}

.cart-input,
.cart-select {
  border: 1px solid #ccc;
  border-radius: 2px;
  font-size: 14px;
  font-weight: 500;
  padding: 10px 15px;
  width: 100%;
}

.cart-input:focus {
  box-shadow: 0 2px 25px 1px rgba(0,0,0,.07);
}

.cart-select {
  
}

.cart-button {
  background-color: #eee;
  border-radius: 2px;
  color: #888;
  display: block;
  font-size: 17px;
  padding: 12px 0;
  text-align: center;
  text-decoration: none;
  width: 100%;
}

.cart-button-step {
  margin-top: 50px;
}

.cart-button-primary {
  background-color: #3E84E0;
  color: #fff;
}

.cart-button-icon {
    vertical-align: bottom;
    width: 16px;
}

.cart-method-container {
  border-bottom: 1px solid #e5e5e5;
  margin-bottom: 20px;
  padding-bottom: 20px;
}

.cart-method-list {
  list-style-type: none;
  margin: 0 0 0 -5px;
  padding: 0;
}

.cart-method-item {
  box-sizing: border-box;
  display: inline-block;
  float: left;
  margin: 0;
  padding: 0 0 0 5px;
  width: 33.3%;
}

.cart-method {
  border: 1px solid #ccc;
  border-radius: 2px;
  cursor: pointer;
  min-height: 60px;
  text-align: center;
}

.cart-method.is-active {
  border: 1px solid #87b2ec;
  box-shadow: 0px 1px 20px 1px rgba(0,0,0,.12);
}

.cart-grid {
  display: -ms-flexbox;
  display: -webkit-flex;
  display: flex;
  /* 1 */
  -ms-flex-wrap: wrap;
  -webkit-flex-wrap: wrap;
  flex-wrap: wrap;
  /* 2 */
  margin: 0 0 0 -5px;
  padding: 0;
  list-style: none;
}
.cart-grid > * {
  padding-left: 5px;
}

[class*='uk-width'] {
  box-sizing: border-box;
  width: 100%;
  /* 1 */
  max-width: 100%;
}

.cart-width-1-1 {
  width: 100%;
}

.cart-width-1-2 {
  width: 50%;
}
!

JS 

              
                                var currentStep;

$('.cart-button-step').on('click', function() {
  if( !fieldsValid() ) return false;
  var currentStep = $(this).data('to-cart-step');
  $('.cart-step').slideUp('fast');
  $('.cart-step-' + currentStep).slideDown('fast');
});

var fieldsValid = function() {
  $('.is-invalid').removeClass('is-invalid');
  var invalidFields = [];
  $('.is-required:visible').each(function(i, el) {
    var $el = $(el)
      field = $el.find('.cart-input');
    
    if(field.val() == "") {
      invalidFields.push(field);
      $el.addClass('is-invalid');
    }
    
  });
  console.log(invalidFields.length);
  return invalidFields.length == 0;
};
!
999px

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