Spróbuj sam - W3.CSS input

<!DOCTYPE html>
<html>
<title>W3.CSS</title>
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="stylesheet" href="/lib/w3.css">
<body><br>

<div class="w3-row-padding">
  <div class="w3-third">
   <input class="w3-input w3-border" type="text" placeholder="One">
  </div>
  <div class="w3-third">
   <input class="w3-input w3-border" type="text" placeholder="Two">
  </div>
  <div class="w3-third">
   <input class="w3-input w3-border" type="text" placeholder="Three">
  </div>
</div>

</body>
</html>