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                <form method='get' action='data:text/plain,Form sumbitted.'>

  <div class='error-message'>
    Please input a valid name.

    <label for='name'>Name:</label><br>
    <input type='text' id='name' name='name' autofocus>
  <input type='submit' id='submit' value='Submit the form'>



                /* input error style */
input.error {
  border: 1px solid FIREBRICK;
  box-shadow: 0 0 4px FIREBRICK;
  background: WHITE;
  color: BLACK;

/* other styles */

.error-message {
  background: FIREBRICK;
  color: WHITE;
  padding: 10px;
  margin-bottom: 20px;
  border-radius: 3px;  

body {
  padding: 50px;
  font-size: 16pt;

fieldset {
  border: none;
  margin: 0;
  padding: 20px 0;


                // Hide the error message by default.

// When cilck on the button.
  // Get the user’s input.
  var value = $('#name').val();
  if (value === "") {
    // Show the error message
    // add error style to input.
    // Stops the default browser behaviors, 
    // which sends the form
    return false;
  } else {
    // Hide the error message
    // Remove the error
    // Empty the input.
    alert("Form submitted");
    // In demo, we block the form submit. In reality, we don’t need the `return false`.
    return false;