style.css

*{
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

.container{
    width: 100%;
    height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
    background-color: #f2f2f2;
}

.form-container{
    width: 500px;
    height: fit-content;
    background-color: white;
    padding: 40px 30px;
    display: flex;
    justify-content: center;
    align-items: center;
    flex-direction: column;
}
h2{
    position: relative;
    margin-bottom: 20px;
    font-size: 2.5rem;
}
h2::before{
    position: absolute;
    content: '';
    bottom: 0;
    left: 50%;
    width: 40px;
    height: 2px;
    background-color: violet;
    transform: translateX(-50%);
}

.form-label{
    margin-bottom: 10px;
    padding-bottom: 20px;
    position: relative;
}

.form-label label{
    display: inline-block;
    margin-bottom: 5px;
    font-size: 1.5rem;
}

.form-label input{
    border: 2px solid #f0f0f0;
    border-radius: 5px;
    display: block;
    font-size: 1.5rem;
    padding: 10px;
    width: 100%;
}

.form-label input:focus{
    outline:0;
    border-color: #777;
}

.noerror input{
    border-color: #2ecc71;
}

.error input{
    border-color: #e74c3c;
}

.form-label i{
    visibility: hidden;
    position: absolute;
    top: 50px;
    right: 10px;
}

.noerror i.fa-check-circle{
    color: #2ecc71;
    visibility: visible;
}

.error i.fa-exclamation-circle{
    color: #e74c3c;
    visibility: visible;
}

.form-label small{
    color: #e74c3c;
    position: absolute;
    bottom: 0;
    left: 0;
    visibility: hidden;
}

.error small{
    visibility: visible;
}

#btn{
    width: 100%;
    padding: 10px 40px;
    font-size: 1.5rem;
    background-color: black;
    color: white;
}

#btn:hover{
    background-color: white;
    color: black;
}