<input type="text" placeholder="Select Me..." />

input:focus {
  background-color: #bbb;
}

/* Additional styling */
input {
  background-color: #ddd;
  display: block;
  width: 240px;
  margin: 12px 0;
  padding: 12px 16px;
  border-radius: 20px;
  border: none;
  outline: none !important;
  transition: 0.1s;
}

html,
body {
  height: 100vh;
  width: 100vw;
  display: flex;
  justify-content: center;
  align-items: center;
  padding: 0;
  margin: 0;
}