style.css

@import url('https://fonts.googleapis.com/css2?family=Roboto+Mono:wght@100&display=swap');

body {
  font-family: Roboto Mono;
  background-color: lightblue;
  text-align: center;
  font-weight: bold;
}
#password {
  margin: auto;
  width: 250px;
}
#password label {
  display: block;
}
#password-input {
  width: 230px;
  padding: 10px;
  margin: 10px 0 5px 0;
}
#password-strength {
  height: 5px;
  width: 100%;
  display: block;
  background-color: #ccc;
}
#password-strength span {
  display: block;
  height: 5px;
  border-radius: 2px;
  transition: all 500ms ease;
}
.strength-0 span {
  background-color: red;
  width: 5%;
}
.strength-1 span {
  background-color: orangered;
  width: 25%;
}
.strength-2 span {
  background-color: orange;
  width: 50%;
}
.strength-3 span {
  background-color: yellowgreen;
  width: 75%;
}
.strength-4 span {
  background-color: green;
  width: 100%;
}