.header-hero {
    background: url("/assets/img/landing-page-bkg-small.jpg") no-repeat center center / cover;
    min-height: 80vh;

    @media (max-width: 767px) and (orientation: landscape) {
        min-height: 350px;
    }

    @media (min-width: 768px) {
        background-image: url("/assets/img/landing-page-bkg.jpg");
    }

    h1 {
        line-height: $header-hero-line-height;
    }

    .display-4 {
        @media (max-width: 767px) {
            font-size: 3rem;
        }
    }
}

.header-hero {
    background: url("/assets/img/landing-page-bkg-small.jpg") no-repeat center center / cover;
    height: 80vh;
    min-height: 80vh;

    @media (max-width: 767px) and (orientation: landscape) {
        min-height: 350px;
    }

    @media (min-width: 768px) {
        background-image: url("/assets/img/landing-page-bkg.jpg");
    }

    h1 {
        line-height: $header-hero-line-height;
    }

    .display-4 {
        @media (max-width: 767px) {
            font-size: 3rem;
        }
    }
}

Add explicit height for hero section.
Add explicit height for hero section.

IE has issues vertically centering without it.
