<div class="container">
  <div class="box -shadow"></div>
  <div class="box"></div>
</div>
.container {
  background: #eee;
  padding: 3%;
  display: flex;
}

.box {
  background: #fff;
  width: 50%;
  float: left;
  height: 200px; 
}

.box.-shadow {
  background: tomato;
  box-shadow: inset -12px 0 15px -10px rgba(0, 0, 0, .6);  
}

External CSS

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External JavaScript

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