viewerjs/test/css/main.css

.container {
  max-width: 640px;
  max-height: 360px;
  margin: 20px auto;
}

.container > ul {
  width: 100%;
  margin: 0;
  padding: 0;
  list-style: none;
  font-size: 0;
}

.container > ul > li {
  display: inline-block;
  width: 50%;
}

.container > img,
.container > ul > li > img {
  max-width: 100%;
}