W3Schools Tryit Editor

<!DOCTYPE html>
<html>
<title>W3.CSS</title>
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="stylesheet" href="https://www.w3schools.com/w3css/5/w3.css">
<body>

<div class="w3-container">
  <h2>Filter Dropdown Click</h2>
  <p>Click on the dropdown and search for a specific link inside the input field.</p>

<div class="w3-dropdown-click">
    <button class="w3-button w3-black" onclick="dropFunction()">Dropdown</button>
    <div class="w3-dropdown-content w3-bar-block w3-card w3-light-grey" id="myDIV">
      <input class="w3-input w3-padding" type="text" placeholder="Search.." id="myInput" onkeyup="filterFunction()">
      <a class="w3-bar-item w3-button" href="#about">About</a>
      <a class="w3-bar-item w3-button" href="#base">Base</a>
      <a class="w3-bar-item w3-button" href="#blog">Blog</a>
      <a class="w3-bar-item w3-button" href="#contact">Contact</a>
      <a class="w3-bar-item w3-button" href="#custom">Custom</a>
      <a class="w3-bar-item w3-button" href="#support">Support</a>
      <a class="w3-bar-item w3-button" href="#tools">Tools</a>
    </div>
  </div>
</div>

// Filter
function filterFunction() {
  var input, filter, ul, li, a, i;
  input = document.getElementById("myInput");
  filter = input.value.toUpperCase();
  div = document.getElementById("myDIV");
  a = div.getElementsByTagName("a");
  for (i = 0; i < a.length; i++) {
    txtValue = a[i].textContent || a[i].innerText;
    if (txtValue.toUpperCase().indexOf(filter) > -1) {
      a[i].style.display = "";
    } else {
      a[i].style.display = "none";
    }
  }
}
</script>

</body>
</html>

​x
 
<!DOCTYPE html><html><title>W3.CSS</title><meta name="viewport" content="width=device-width, initial-scale=1"><link rel="stylesheet" href="https://www.w3schools.com/w3css/5/w3.css"><body>​<div class="w3-container">  <h2>Filter Dropdown Click</h2>  <p>Click on the dropdown and search for a specific link inside the input field.</p>​  <div class="w3-dropdown-click">    <button class="w3-button w3-black" onclick="dropFunction()">Dropdown</button>    <div class="w3-dropdown-content w3-bar-block w3-card w3-light-grey" id="myDIV">      <input class="w3-input w3-padding" type="text" placeholder="Search.." id="myInput" onkeyup="filterFunction()">      <a class="w3-bar-item w3-button" href="#about">About</a>      <a class="w3-bar-item w3-button" href="#base">Base</a>      <a class="w3-bar-item w3-button" href="#blog">Blog</a>      <a class="w3-bar-item w3-button" href="#contact">Contact</a>      <a class="w3-bar-item w3-button" href="#custom">Custom</a>      <a class="w3-bar-item w3-button" href="#support">Support</a>      <a class="w3-bar-item w3-button" href="#tools">Tools</a>    </div>  </div></div>​<script>// Dropdownfunction dropFunction() {  var x = document.getElementById("myDIV");  if (x.className.indexOf("w3-show") == -1) {    x.className += " w3-show";  } else {    x.className = x.className.replace(" w3-show", "");  }}​// Filterfunction filterFunction() {  var input, filter, ul, li, a, i;  input = document.getElementById("myInput");  filter = input.value.toUpperCase();  div = document.getElementById("myDIV");