<div class="container">
  <div id="marketing" class="section">
    <div class="content">
      <h1>Marketing</h1>
    </div>
    <div class="overlay"></div>
  </div>
  <div id="technology" class="section">
    <div class="content">
      <h1>Technology</h1>
    </div>
    <div class="overlay"></div>
  </div>
  <div id="advertising" class="section">
    <div class="content">
      <h1>Advertising</h1>
    </div>
    <div class="overlay"></div>
  </div>
</div>

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  padding: 0;
  font-family: 'Montserrat', sans-serif;
}

.container {
  display: flex;
  height: 100vh;
}

.section {
  flex: 1;
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100%;
  overflow: hidden;
  background-size: cover;
  background-position: center;
  color: #fff;
  transition: flex .4s ease;
  position: relative;
}

.section .overlay {
  background-color: rgba(0, 0, 0, 0.7);
  width: 100%;
  height: 100%;
  position: absolute;
  transition: background-color .8s ease;
}

.section .content {
  z-index: 2;
}

.section:hover {
  flex: 2;
}

.section:hover .overlay {
  background-color: rgba(0, 0, 0, 0.95);
}

#marketing {
  background-image: url(https://images.unsplash.com/photo-1522205987242-8e22924ab42a?ixlib=rb-0.3.5&ixid=eyJhcHBfaWQiOjEyMDd9&s=c0f679eb8f15705d46ea90008f39642b&auto=format&fit=crop&w=500&q=60);
}


#technology {
  background-image: url(https://images.unsplash.com/photo-1530893609608-32a9af3aa95c?ixlib=rb-0.3.5&ixid=eyJhcHBfaWQiOjEyMDd9&s=fe6b92f88f55824e64a1bae15f5bf52a&auto=format&fit=crop&w=500&q=60);
}

#advertising {
  background-image: url(https://images.unsplash.com/photo-1517799094725-e3453440724e?ixlib=rb-0.3.5&ixid=eyJhcHBfaWQiOjEyMDd9&s=353f3663a9fae75773d2942aeb37c2c8&auto=format&fit=crop&w=500&q=60);
}

/*
  Nothing to see here :)
  ---
  Explanation of the code: https://youtu.be/Iz-uUuTpohk
  ---
*/