@import url('https://fonts.googleapis.com/css2?family=Roboto:wght@400;700&display=swap');

* {
  box-sizing: border-box;
}

body {
  font-family: 'Roboto', sans-serif;
  display: flex;
  align-items: center;
  justify-content: center;
  height: 100vh;
  overflow: hidden;
  margin: 0;
  background-color: blue;
}

.container {
  position: relative;
  height: 50px;
}
.input {
  background-color: aliceblue;
  height: 50px;
  border: 0;
  width: 50px;
  font-size: 20px;
  transition: width 0.4s ease;
}
.input:focus {
  outline: 0;
}
.btn {
  background-color: aliceblue;
  height: 50px;
  width: 50px;
  border: 0;
  position: absolute;
  top: 0;
  left: 0;
  cursor: pointer;
  font-size: 24px;
  transition: transform 0.4s ease;
}

.container.active input {
  width: 200px;
}
.container.active .btn {
  transform: translateX(199px);
}