style.css

@import url('https://fonts.googleapis.com/css2?family=Poppins:ital,wght@0,100;0,200;0,300;0,400;0,500;0,600;1,100;1,200;1,300;1,400;1,500&family=Roboto:wght@400;500;700&display=swap');
* {
  margin: 0;
  padding: 0;
  outline: none;
  text-transform: capitalize;
  font-family: 'Poppins', sans-serif;
}
:root {
  --black: #000000;
  --red: rgb(255, 0, 0);
  --light-color: #666;
  --light-gray: #f1f1f1e0;
  --primary-go: #ffffff;
}
body {
  height: 100vh;
  background-color: var(--black);
}
a {
  text-decoration: none;
  color: var(--light-color);
  font-size: small;
}
.flex {
  display: flex;
  align-items: center;
  justify-content: center;
}
.container {
  border-radius: 1rem;
  padding: 3rem 2rem 3rem 2rem;
  flex-direction: column;
  background-color: var(--primary-go);
}
.container h3 {
  font-size: 1.8rem;
}
.container input,
button {
  width: 15rem;
  height: 2.5rem;
  margin: 0.4rem;
  border: 0;
  font-weight: 500;
  font-size: smaller;
  border-radius: 0.5rem;
  cursor: pointer;
}
.container input {
  background-color: var(--light-gray);
  text-transform: lowercase;
  font-weight: normal;
  padding-left: 1rem;
}
.error {
  width: 15rem;
  height: 2rem;
  font-size: small;
  color: var(--red);
}
.name {
  display: none;
}
.name.active {
  display: flex;
}
.email {
  display: none;
}
.email.active {
  display: flex;
}
.pass {
  display: none;
}
.pass.active {
  display: flex;
}
.container .signup {
  color: var(--primary-go);
  background-color: var(--black);
}
.container h5 {
  font-size: 0.7rem;
  color: var(--light-color);
}
.back {
  position: relative;
  top: -1.5rem;
  left: -9rem;
}
@media (max-width: 450px) {
  .container {
    width: 100%;
    height: 100%;
    border-radius: 0;
  }
  .container h3 {
    font-size: 1.6rem;
  }
  .container input,
  button {
    width: 16rem;
    height: 2.5rem;
    border-radius: 0.5rem;
  }
  .back {
    position: absolute;
    top: 2rem;
    left: 2rem;
  }
}