Ratio Full Screen Box

by Vladimir Kutepov

HTML

<div class="header"></div>
<div class="container">
  <div class="box"></div>
  <div class="bar"></div>
</div>

CSS

body {
  margin: 0;
}

.box {
  margin: 0 auto;
  height: calc(100vh - 100px - 80px);
  width: calc(177.78vh - 178px - 142px); /* 16/9 = 1.778 */
  max-width: 100%;
  max-height: 56.25vw; /* 100/1.778 = 56.25 */
  min-height: 180px; /* 320 * 9/16 = 180 */
  min-width: 320px;
  background: yellow url(https://upload.wikimedia.org/wikipedia/en/b/be/Locator_Grid.png) no-repeat 50% 50%;
  background-size: cover;
}

.bar {
  background: orange;
  height: 80px;
}


@media (min-width: 700px) {
  .header {
    height: 100px;
    background: gray;
  }
}

@media (max-width: 699px) {
  .container {
    height: 100vh;
    display: flex;
    flex-direction: column;
    justify-content: center;
  }
  
  .box {
    height: calc(100vh - 80px);
    width: calc(177.78vh - 142px); /* 16/9 = 1.778 */
  }
}