@media (-moz-bool-pref: "zen.tabs.vertical") {
  /* Tab Borders Based on Preference */
  .tabbrowser-tab:not([pinned]):is([multiselected="true"], [selected]) {
    &:has(#uc-tabs[uc-tabs-preferred_color="primary"]) .tab-background {
      border: 2px solid var(--zen-colors-primary) !important;
    }
    &:has(#uc-tabs[uc-tabs-preferred_color="secondary"]) .tab-background {
      border: 2px solid var(--zen-colors-secondary) !important;
    }
    &:has(#uc-tabs[uc-tabs-preferred_color="tertiary"]) .tab-background {
      border: 2px solid var(--zen-colors-tertiary) !important;
    }
    &:has(#uc-tabs[uc-tabs-preferred_color="border"]) .tab-background {
      border: 2px solid var(--zen-colors-border) !important;
    }
    &:has(#uc-tabs[uc-tabs-preferred_color="custom"]) .tab-background {
      @media (prefers-color-scheme: light) {
        border: 2px solid var(--uc-tabs-preferred_color, #000000) !important; /* Fallback to black */
      }
      @media (prefers-color-scheme: dark) {
        border: 2px solid var(--uc-tabs-preferred_color, #ffffff) !important; /* Fallback to white */
      }
    }
  }

  /* Background Modification for Selected Tab */
  #tabbrowser-tabs {
    & .tabbrowser-tab {
      &[selected] .tab-background {
        background: color-mix(
          in srgb,
          var(--zen-colors-secondary) 40%,
          transparent
        ) !important;
      }
    }
  }

  /* Dimming Tab Text When Unloaded */
  @media (-moz-bool-pref: "uc.tabs.dim_unloaded") {
    #tabbrowser-tabs {
      & .tabbrowser-tab {
        @media (-moz-bool-pref: "zen.tabs.dim-pending") {
          &[pending="true"] .tab-text {
            opacity: 0.5; /* Dimmed text for pending tabs */
          }
        }
      }
    }
  }
}