<div class="flex-box">
	  <div class="thumnail-left-box">
	  <img src="https://placehold.jp/150x150.png">
	  </div>
	  <ul class="thumnail-right-box flex-box">
	  <li><img src="https://placehold.jp/50x50.png"></li>
	  <li><img src="https://placehold.jp/50x50.png"></li>
	  <li><img src="https://placehold.jp/50x50.png"></li>
	  <li><img src="https://placehold.jp/50x50.png"></li>
	  <li><img src="https://placehold.jp/50x50.png"></li>
	  <li><img src="https://placehold.jp/50x50.png"></li>
	  <li><img src="https://placehold.jp/50x50.png"></li>
	  <li><img src="https://placehold.jp/50x50.png"></li>
	  <li><img src="https://placehold.jp/50x50.png"></li>
	  <li><img src="https://placehold.jp/50x50.png"></li>
	  </ul>
	</div>
.flex-box {
  display: flex;
  flex-wrap: wrap;
}

.flex-box img {
  vertical-align: top;
}

.thumnail-left-box {
  width: 70%;
  margin: 0;
  padding: 0 0 2.5%;
}

.thumnail-left-box img {
  width: 100%;
}

.thumnail-right-box {
  width: 30%;
  margin: 0;
  padding: 0;
  list-style: none;
}

.thumnail-right-box li {
  display: flex;
  flex-wrap: wrap;
  width: 40%;
  margin: 0 0 0 auto;
}

.thumnail-right-box li img {
  width: 100%;
  margin: 0 0 auto;
}

External CSS

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External JavaScript

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