style.css

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
  }
  
  .main_div {
    width: 100%;
    height: 100vh;
    position: relative;
  }
  
  .box {
    width: 400px;
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    padding: 50px;
    background: rgba(0, 0, 0, 0.8);
    border-radius: 10px;
  }
  
  .box h1 {
    margin-bottom: 25px;
    color: #fff;
    text-align: center;
    text-transform: capitalize;
  }
  
  .box .input-box {
    position: relative;
  }
  
  .box .input-box input {
    width: 100%;
    padding: 10px;
    font-size: 16px;
    letter-spacing: 1px;
    color: #fff;
    margin-bottom: 30px;
    border: none;
    border-bottom: 1px solid #fff;
    background: transparent;
    outline: none;
  }
  
  .box .input-box label {
    position: absolute;
    top: 0;
    left: 0;
    letter-spacing: 1px;
    padding: 10px 0;
    font-size: 16px;
    color: #fff;
    transition: 0.5s;
  }
  
  .box input[type="submit"] {
    background: transparent;
    border: none;
    outline: none;
    color: #fff;
    background: #03a9f4;
    padding: 9px 18px;
    border-radius: 5px;
    font-size: 14px;
  }
  
  .box .input-box input:focus~label, .box .input-box input:valid~label {
    top: -20px;
    left: 0;
    font-size: 12px;
    color: #03a9f4;
  }