HTMLify

body {
  height: 100vh;
  display: flex;
  flex-direction: column;
  align-items: center;
  overflow-x: hidden;
}
.container {
  display: flex;
}
.l-container {
  position: relative;
  flex: 1;
  background-color: #ffd4b8;
  height: 100vh;
  width: 100vw;
  overflow: hidden;
  transition: flex 0.5s ease-in-out;
}
.l-container::after {
  content: "";
  position: absolute;
  background-image: url(./sad.png);
  height: 100%;
  width: 100%;
  bottom: 0;
  left: 50%;
  background-position: center;
  background-repeat: no-repeat;
  background-size: cover;
}
.r-container {
  position: relative;
  flex: 1;
  background-color: #cfffd0;
  width: 100vw;
  overflow: hidden;
  transition: flex 0.5s ease-in-out;
}
.r-container::after {
  content: "";
  position: absolute;
  background-image: url(./happy.png);
  height: 100%;
  width: 100%;
  bottom: 0;
  right: 50%;
  background-position: center;
  background-repeat: no-repeat;
  background-size: cover;
}
.l-container.active {
  flex: 2;
}
.r-container.active {
  flex: 2;
}