MediaWiki:Citizen.css

/* All CSS here will be loaded for users of the Citizen skin */
:root.skin-theme-clientpref-dark {
    --color-surface-0: #050e1b;
    --color-surface-1: #0d1014;
    --color-base: #fff;
    --color-base--emphasized: #808080;
    --color-base--subtle: #162132;
}
:root.skin-theme-clientpref-os {
    --color-surface-0: #050e1b;
    --color-surface-1: #0d1014;
    --color-base: #fff;
    --color-base--emphasized: #808080;
    --color-base--subtle: #162132;
}

.citizen-page-container {
    background-image: url("resources/assets/hero.webp");
    background-repeat: no-repeat;
    background-position: center;
    background-attachment: fixed;
}