<header class="header">
  <div class="header__title">
  <div class="header__reference">
    <ul class="reference-list">
      <li><a class="reference-list__link" href="https://developer.mozilla.org/en-US/docs/Web/CSS/filter-function/drop-shadow">MDN reference</a></li>
      <li><a class="reference-list__link" href="https://caniuse.com/#feat=css-filters">caniuse Support</a></li>

  <div class="example">
      In this example, we have a blurry pink Space Invader hiding behind our green one! What's especially cool about this is that the green Space Invader is a rectangular raster PNG image, but <code>drop-shadow()</code> works with the image's transparent areas. 
      If you hover over the example area, we're able to animate the filter effect to increase the blur effect and darken the pink color:

    <div class="example__demo example__demo--drop-shadow">
        alt="A lime green, 3D Space Invader from the game of the same name." 
        src="https://s3-us-west-2.amazonaws.com/s.cdpn.io/11907/space-invader.png" />
// Demo
.space-invader {
  height: auto;
  filter: drop-shadow(3rem 0 0.5rem #e486da);
  margin-right: 2rem;
  width: 50%;
    filter var(--transition-duration-long) ease-in-out,
    transform var(--transition-duration-long) ease-in-out;

.example__demo--drop-shadow:hover {
  .space-invader {
    transform: translateX(-2rem);
    filter: drop-shadow(7rem 0 1rem #965990);    

// Pen Setup
.example__demo--drop-shadow {
  background-color: var(--color-cinder);
  background-size: cover;
  display: flex;
  flex-direction: row;
  justify-content: center;
  padding-top: 4rem;
  padding-bottom: 4rem;
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External CSS

  1. https://codepen.io/ericwbailey/pen/vMXWgz.scss

External JavaScript

This Pen doesn't use any external JavaScript resources.