Toolbar not fully themed in tab mode on Linux · Issue #1999 · zotero/zotero

You might find this workaround useful:

1. Close Zotero.
2. Open your Zotero profile folder.
3. Inside this folder, create a sub-folder named chrome.
4. Inside the folder chrome, create a file named userChrome.css with the content below.
5. Save. Reopen Zotero and enjoy.

Tested on Linux Mint 21.2 with the default dark theme.

.tabs::before,
.tabs::after {
    border-color: var(--tabs-border-color, rgba(0,0,0,.3)) !important;
}

.tab {
    background: inherit !important;
    color: inherit !important;
}
#tab-bar-container .tab:not(:last-child) {
    border-color: var(--tabs-border-color, rgba(0,0,0,.3)) !important;
}

#tab-bar-container .tab.selected {
    background: inherit !important;
    border-color: var(--tabs-border-color, rgba(0,0,0,.3)) !important;
    border-top-color: var(--tabline-color, #0a84ff) !important;
}

#tab-bar-container .tab:not(.selected) {
    border-bottom-color: var(--tabs-border-color, rgba(0,0,0,.3)) !important;
}

#tab-bar-container .tab:not(:first-child) .tab-close {
  filter: invert(0.7);
}

#zotero-toolbar {
    background: inherit !important;
    border-bottom: inherit !important;
}