style.css

.header {
    width: 100%;
    height: 80px;
    /*background-color: aqua;*/
    position: fixed;
    z-index: 3;
}

.logo {
    width: 200px;
    height: 40px;
    background-image: url(../img/ienlab_logo_bk_transparent.png);
    background-size: contain;
    background-repeat: no-repeat;
    position: absolute;
    left: 50%;
    transform: translateX(-50%);
    margin: 20px;
    z-index: 4;
    transition: background-image 0.2s ease-in-out;
}

.logo:hover {
    background-image: url(../img/ienlab_logo_cl.png)
}

i.fab {
    font-size: 30px;
    margin: 10px;
}


.page {
    height: 100vh;
    overflow: hidden;
    background-attachment: fixed;
    background-size: cover;
}


.page.one {
    background-image: url(../img/bg_main.png);
}

.page.one .overlay {
    background-color: #000000;
    background-size: cover;
    /*position: fixed;*/
    z-index: 2;
    width: 100%;
    height: 100%;
    opacity: 0.5;
}

.page.two {
    background-image: url(../img/bg_bp.png);
}

.page.three {
    background-image: url(../img/bg_ir.png);
}

.page.four {
    background-image: url(../img/bg_ar.png);
}