试一试 - W3.CSS ref_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>      
<input class="w3-input" type="email" required>
<label class="w3-label w3-validate">Email</label>

<br>      
<textarea class="w3-input"></textarea>
<label class="w3-label">Subject</label>

<br>
<input id="sugar" class="w3-check" type="checkbox">
<label class="w3-validate">Sugar</label>

<br>
<input id="lemon" class="w3-check" type="checkbox" disabled>
<label class="w3-validate">Lemon (Disabled)</label>

<br>
<input id="female" class="w3-radio" type="radio" name="gender" value="female">
<label class="w3-validate">Female</label>

<br>
<input id="unknown" class="w3-radio" type="radio" name="gender" value="" disabled>
<label class="w3-validate"> Don't know (Disabled)</label>
  
</form>

</body>
</html>