html/forms/hidden-input-example/index.html

<!DOCTYPE html>
<html lang="en-US">
  <head>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width">
    <title>&lt;input type="hidden"&gt; example</title>
  <style>
    html {
      font-family: sans-serif;
    }

    form {
      width: 500px;
    }

    div {
      display: flex;
      margin-bottom: 10px;
    }

    label {
      flex: 2;
      line-height: 2;
      text-align: right;
      padding-right: 20px;
    }

    input, textarea {
      flex: 7;
      font-family: sans-serif;
      font-size: 1.1rem;
      padding: 5px;
    }

    textarea {
      height: 60px;
    }

  </style>
  </head>
<body>
  <form>
    <div>
      <label for="title">Post title:</label>
      <input type="text" id="title" name="title" value="My excellent blog post">
    </div>
    <div>
      <label for="content">Post content:</label>
      <textarea id="content" name="content">
This is the content of my excellent blog post. I hope you enjoy it!
      </textarea>
    </div>
    <div>
      <button type="submit">Update post</button>
    </div>
    <input type="hidden" id="postId" name="postId" value="34657">
  </form>
</body>