zotero/scss/base/_base.scss

:root {
    font-family: system-ui, -apple-system, sans-serif;
    font-size: 13px;
    font-style: normal;
    line-height: 1.3333333333;
    @media (-moz-platform: windows) {
        --color-accent: var(--accent-blue);
        @include light-dark(--color-focus-border, #000, #fff);
        --width-focus-border: 2px;
    }
    @media (-moz-platform: macos) {
        --color-accent: SelectedItem;
        --color-focus-border: color-mix(in srgb, var(--color-accent) 50%, transparent);
        --width-focus-border: 3px;
    }
    @media (-moz-platform: linux) {
        --color-accent: SelectedItem;
        --color-focus-border: var(--color-accent);
        --width-focus-border: 2px;
    }
    --color-focus-search: color-mix(in srgb, var(--color-accent) 50%, transparent);
}

#zotero-collections-pane, #zotero-item-pane {
    background: var(--material-sidepane);
}

#zotero-title-bar {
    border-bottom: var(--material-panedivider);
}