<div class="demo-container d-flex justify-content-center">

 <form action="" method="post"> 
 
  <div class="radio-buttons-container">
  
   <input type="radio" id="star_5" name="stars" value="5" <?=$_POST['stars']=="5" ? "checked" : ""?> /> <label for="star_5" title="Awesome"></label>
   
   <input type="radio" id="star_4.5" name="stars" value="4.5" <?=$_POST['stars']=="4.5" ? "checked" : ""?> /> <label for="star_4.5" class="half"></label>

   <input type="radio" id="star_4" name="stars" value="4" <?=$_POST['stars']=="4" ? "checked" : ""?> /> <label for="star_4"></label>

   <input type="radio" id="star_3.5" name="stars" value="3.5" <?=$_POST['stars']=="3.5" ? "checked" : ""?> /> <label for="star_3.5" class="half"></label>

   <input type="radio" id="star_3" name="stars" value="3" <?=$_POST['stars']=="3" ? "checked" : ""?> /> <label for="star_3"></label>

   <input type="radio" id="star_2.5" name="stars" value="2.5" <?=$_POST['stars']=="2.5" ? "checked" : ""?> /> <label for="star_2.5" class="half"></label>

   <input type="radio" id="star_2" name="stars" value="2" <?=$_POST['stars']=="2" ? "checked" : ""?> /> <label for="star_2"></label>

   <input type="radio" id="star_1.5" name="stars" value="1.5" <?=$_POST['stars']=="1.5" ? "checked" : ""?> /> <label for="star_1.5" class="half"></label>

   <input type="radio" id="star_1" name="stars" value="1" <?=$_POST['stars']=="1" ? "checked" : ""?> /> <label for="star_1"></label>

   <input type="radio" id="star_0.5" name="stars" value="0.5" <?=$_POST['stars']=="0.5" ? "checked" : ""?> /> <label for="star_0.5" class="half"></label>

 </div> 

<div class="container my-3">
<div class="col-md-12 text-center">

<input class="btn btn-primary" type="submit" name="submit" value="Submit">
</div>

  </div>

 </form>
</div>

<?php

  if(isset($_POST["submit"])){
  
   if(!empty($_POST["stars"])) {
    echo "<div class='results-content'>Your selected star value is: <strong>" . $_POST["stars"] . "</strong></div>"; 
} 

  else {
   echo "<div class='results-content'>Please select a star value </div>";
}

}
?> 
</div>