form.css

 body{
            font-family: Arial, Helvetica, sans-serif;
            background-image: linear-gradient(to right, rgb(20, 147, 220), rgb(17, 54, 71));
        }
        .box{
            color: white;
            position: absolute;
            top: 50%;
            left: 50%;
            transform: translate(-50%,-50%);
            background-color: rgba(0, 0, 0, 0.6);
            padding: 15px;
            border-radius: 15px;
            width: 20%;
        }
        fieldset{
            border: 3px solid dodgerblue;
        }
        legend{
            border: 1px solid dodgerblue;
            padding: 10px;
            text-align: center;
            background-color: dodgerblue;
            border-radius: 8px;
        }
        .inputBox{
            position: relative;
        }
        .inputUser{
            background: none;
            border: none;
            border-bottom: 1px solid white;
            outline: none;
            color: white;
            font-size: 15px;
            width: 100%;
            letter-spacing: 2px;
        }
        .labelInput{
            position: absolute;
            top: 0px;
            left: 0px;
            pointer-events: none;
            transition: .5s;
        }
        .inputUser:focus ~ .labelInput,
        .inputUser:valid ~ .labelInput{
            top: -20px;
            font-size: 12px;
            color: dodgerblue;
        }
        #data_nascimento{
            border: none;
            padding: 8px;
            border-radius: 10px;
            outline: none;
            font-size: 15px;
        }
        #submit{
            background-image: linear-gradient(to right,rgb(0, 92, 197), rgb(90, 20, 220));
            width: 100%;
            border: none;
            padding: 15px;
            color: white;
            font-size: 15px;
            cursor: pointer;
            border-radius: 10px;
            text-decoration: none;
        }
        #submit:hover{
            background-image: linear-gradient(to right,rgb(0, 80, 172), rgb(80, 19, 195));
        }
        .button a{
            text-decoration: none;
        }