What is wrong with this "box-shadow" in IE?

Question

This property drives me crazy. box-shadow is still not working in IE11 (and Edge). In other browsers it is fine. Can somebody help me with this? I ran out of ideas.

.select--options {
  border-collapse: separate; 
  display: block; 
  box-shadow: 8px 8px 18px #00000021;
  -webkit-box-shadow: 8px 8px 18px #00000021;
  -moz-box-shadow: 8px 8px 18px #00000021;
  -ms-box-shadow: 8px 8px 18px #00000021;
}

<div class="select--options">
  <div class="option">Test 1</div>
  <div class="option">Test 2</div>
</div>

Answer 1

Problem solved, IE has a problem with 8-digit hex code (#00000021 - I didn't notice that). #000021 etc. works fine.