style.css

body{
    margin: 0%;
    padding: 0%;
    background: url(img1.jpg) no-repeat;
    background-size: cover;
    display: grid;
    align-items: center;
    justify-content: center;
    height: 100vh;
    font-family: 'Lucida Sans', 'Lucida Sans Regular', 'Lucida Grande', 'Lucida Sans Unicode', Geneva, Verdana, sans-serif;
}

.container{
    width:50rem;
    height: 35rem;
    box-shadow: 0 0 1rem rgba(0, 0, 0, 2);
    border-radius: 5px;
}

.container:hover{
    background-color: rgba(0, 0, 0, 0.55);
}

.box{
    align-items: center;
    padding: 15px;;
}

::placeholder{
    color: #fff;
    opacity: 0.4;
}

#firstName{
    width: 350px;
    height: 2rem;
    margin-top: 25px;
    margin: 15px;
    align-self: center;
    text-align: center;
    padding: 0.5rem;
    border-radius: 15px;
    background-color: rgba(0, 0, 0, 0.4);
    color: #fff;
    font-weight: bold;
    font-size: 1rem;
    transition: transition(45%, 45%);
    border: 0;
    margin-left: 200px;
    margin-top: 50px;
}

#firstName:focus{
    border-collapse: collapse;
}

#lastName{
    width: 350px;
    height: 2rem;
    margin: 15px;
    align-content: center;
    text-align: center;
    padding: 0.5rem;
    border-radius: 15px;
    background-color: rgba(0, 0, 0, 0.4);
    color: #fff;
    font-weight: bold;
    font-size: 1rem;
    border: 0;
    margin-left: 200px;
    margin-top: 40px;
}

#mobile{
    width: 350px;
    height: 2rem;
    margin: 15px;
    align-content: center;
    text-align: center;
    padding: 0.5rem;
    border-radius: 15px;
    background-color: rgba(0, 0, 0, 0.4);
    color: #fff;
    font-weight: bold;
    font-size: 1rem;
    border: 0;
    margin-left: 200px;
    margin-top: 40px;
}

#mail{
    width: 350px;
    height: 2rem;
    margin: 15px;
    align-content: center;
    text-align: center;
    padding: 0.5rem;
    border-radius: 15px;
    background-color: rgba(0, 0, 0, 0.4);
    color: #fff;
    font-weight: bold;
    font-size: 1rem;
    border: 0;
    margin-left: 200px;
    margin-top: 40px;
}

#btn{
    width: 100px;
    height: 45px;
    border-radius: 50px;
    border: 0;
    background-color: rgba(0, 0, 0, 0.55);
    color: #fff;
    font-weight: bold;
    font-size: 1.2rem;
    font-stretch: wider;
    margin-top: 50px;
    margin-left: 350px;
}