<div class="container">

<img src="data:image/svg+xml;charset=utf-8,%3Csvg xmlns%3D'http%3A%2F%2Fwww.w3.org%2F2000%2Fsvg' viewBox%3D'0 0 320 180'%2F%3E" 
     data-src="http://satyr.io/320x180" width="320" height="180" alt="Image…">
  
</div>
/* etc: */

img {
  max-width: 100%;
  height: auto;
  background: lightgrey;
}

.container {
  max-width: 320px;
}

External CSS

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External JavaScript

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