This is a very simple payment gateway. You can develop this and use this structure for your own websites. I have used Java, HTML and CSS only. . .
Java code
function loadData(name){ if(name == "btn1") { document.getElementById("about").innerHTML = "hello" ; } else { alert("Invalid!!!"); }
HTML code
<!-- custom css file link -->
<link rel="stylesheet" href="css/style.css">
<form action="">
<div class="row">
<div class="col">
<h3 class="title">billing address</h3>
<div class="inputBox">
<span>full name :</span>
<input type="text" placeholder="john deo">
</div>
<div class="inputBox">
<span>email :</span>
<input type="email" placeholder="example@example.com">
</div>
<div class="inputBox">
<span>address :</span>
<input type="text" placeholder="room - street - locality">
</div>
<div class="inputBox">
<span>city :</span>
<input type="text" placeholder="mumbai">
</div>
<div class="flex">
<div class="inputBox">
<span>state :</span>
<input type="text" placeholder="india">
</div>
<div class="inputBox">
<span>zip code :</span>
<input type="text" placeholder="123 456">
</div>
</div>
</div>
<div class="col">
<h3 class="title">payment</h3>
<div class="inputBox">
<span>cards accepted :</span>
<img src="images/card_img.png" alt="">
</div>
<div class="inputBox">
<span>name on card :</span>
<input type="text" placeholder="mr. john deo">
</div>
<div class="inputBox">
<span>credit card number :</span>
<input type="number" placeholder="1111-2222-3333-4444">
</div>
<div class="inputBox">
<span>exp month :</span>
<input type="text" placeholder="january">
</div>
<div class="flex">
<div class="inputBox">
<span>exp year :</span>
<input type="number" placeholder="2022">
</div>
<div class="inputBox">
<span>CVV :</span>
<input type="text" placeholder="1234">
</div>
</div>
</div>
</div>
<input type="submit" value="proceed to checkout" class="submit-btn">
</form>