IMG FILL ISSUE

HTML

<div class="container">
  <div class="sub-container">
    <div class="first-container">
      A
    </div>
    <div class="second-container">
      <img src="https://internationalbarcodes.net/wp-content/uploads/2017/04/QR%20code%20example.jpg" />
    </div>
  </div>

</div>

SCSS

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

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

/* ADJUSTMENT HERE */
.sub-container > div {
  flex: 1;
}

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

.second-container {
  background-color: yellow;
}

.second-container > img {
  max-height: 100%;
  max-width: 100%;
  object-fit: scale-down;
}