isset is not working on submit

This is a 5-star rating form and I am trying to make it work.

<div class="stars">
  <form>
    <input class="star star-5" id="star-5" type="radio" name="star" value="5"/>
    <label class="star star-5" for="star-5"></label>
    <input class="star star-4" id="star-4" type="radio" name="star" value="4"/>
    <label class="star star-4" for="star-4"></label>
    <input class="star star-3" id="star-3" type="radio" name="star" value="3"/>
    <label class="star star-3" for="star-3"></label>
    <input class="star star-2" id="star-2" type="radio" name="star" value="2"/>
    <label class="star star-2" for="star-2"></label>
    <input class="star star-1" id="star-1" type="radio" name="star" value="1"/>
    <label class="star star-1" for="star-1"></label>
    <button class="button" type="submit" name="submit" value="submit">Submit</button>

  </form>
</div>

When I press the submit button nothing happens. The code does not move into the if statement, though it should since submit is not longer null.

<?php
if(isset($_POST['submit'])){
    $rating = $_POST['star'];
    echo "hello";
    echo $rating;
}
?>