Get your own website Result Size: 625 x 534
x
 
<!DOCTYPE html>
<html>
<head>
<style> 
input {
  width: 100%;
}
</style>
</head>
<body>
<h2>A full-width input field</h2>
<form>
  <label for="fname">First Name</label>
  <input type="text" id="fname" name="fname">
</form>
</body>
</html>