<!DOCTYPE html>
<html>
<head>
<title>Title of the document</title>
<style>
input {
border: 2px solid #cccccc;
}
input:invalid:focus {
background-color: lightblue;
}
</style>
</head>
<body>
<form action="/form/submit" method="post">
<label for="password">Password:
<input type="password" name="password" id="password" required minlength="8">
</label>
<input type="submit" value="Go">
</form>
</body>
</html>