Responsive landing page using Flexbox and pseudo elements

For the image, I did something like this, I hope that helps:

            <div class="image-container">
                <img class="main-image" src="images/image-header-mobile.jpg" alt="">
            </div>

.image-container {
  display: inherit;
  position: relative;
  width: 100%;
  border-radius: 0 10px 10px 0;
  background-color: hsl(277, 64%, 61%);
}
.main-image {
  width: 100%;
  height: 100%;
  position: relative;
  background-size: cover;
  border-radius: 0 10px 10px 0;
  mix-blend-mode: multiply;
  opacity: 0.75;
}