IMG FILL ISSUE

HTML

<div class="container">
  <div class="sub-container">
    <div class="first-container">
      A
    </div>
    <div class="second-container">

    </div>
  </div>

</div>

SCSS

.container {
  display: flex;
  min-height: 300px;
  width: 500px;
  flex: 1;
}

.sub-container {
  flex: 1;
  display: flex;
  flex-direction: row;
}

.sub-container>div {
  flex-grow: 1;
}

.first-container {
  background-color: blue;
}

.second-container {
      background: url(https://internationalbarcodes.net/wp-content/uploads/2017/04/QR%20code%20example.jpg);
    background-repeat: no-repeat;
    background-size: 100% 100%;
  
}