#tabbrowser-tabs {
  & .tab-background {
    position: relative;
  }

& .tab-context-line {
    position: absolute;
    width: var(--container-line-width) !important;
    height: var(--container-line-height) !important;
    inset: var(--container-line-inset) !important;
  }
}

/* DEFAULTS */
:root {
  --container-line-thickness: 3px;
  --container-line-length: 100%;
  --container-underline-length: 2rem; /* expanded + on bottom */

--container-line-pos-left: 0 auto 0 0;
  --container-line-pos-right: 0 0 0 auto;

--container-line-inset: var(--container-line-pos-left);
  --container-line-width: var(--container-line-thickness);
  --container-line-height: var(--container-line-length);
}

/* THICKNESS SETTINGS */
:root {
  :has(#theme-Container-Tab-Tweaks[uc-container-tweaks-width="thin"]) {
    --container-line-thickness: 2px;
  }

&:has(#theme-Container-Tab-Tweaks[uc-container-tweaks-width="thick"]) {
    --container-line-thickness: 5px;
  }
}

/* RIGHT SIDE ALIGN TOGGLE */
:root {
  @media (-moz-bool-pref: "uc.container-tweaks.align.right") {
    --container-line-inset: var(--container-line-pos-right);
  }
}

/* ALIGN TO BOTTOM ALWAYS */
:root {
  &:has(#theme-Container-Tab-Tweaks[uc-container-tweaks-essentials="always"])
    #zen-essentials-container {
    --container-line-length: var(--container-underline-length);
    --container-center-offset: calc(var(--container-line-length) / 2);
    --container-line-pos-bottom: auto calc(50% - var(--container-center-offset))
      0 auto;

--container-line-inset: var(--container-line-pos-bottom);
    --container-line-width: var(--container-line-length);
    --container-line-height: var(--container-line-thickness);
  }

&:has(#theme-Container-Tab-Tweaks[uc-container-tweaks-pins="always"])
    #vertical-pinned-tabs-container {
    --container-line-length: var(--container-underline-length);
    --container-center-offset: calc(var(--container-line-length) / 2);
    --container-line-pos-bottom: auto calc(50% - var(--container-center-offset))
      0 auto;

--container-line-inset: var(--container-line-pos-bottom);
    --container-line-width: var(--container-line-length);
    --container-line-height: var(--container-line-thickness);
  }
}

/* ALIGN TO BOTTOM WHEN EXPANDED */
:root {
  @media (-moz-bool-pref: "zen.view.sidebar-expanded") {
    :has(#theme-Container-Tab-Tweaks[uc-container-tweaks-essentials="expanded"])
      #zen-essentials-container {
      --container-line-length: var(--container-underline-length);
      --container-center-offset: calc(var(--container-line-length) / 2);
      --container-line-pos-bottom: auto
        calc(50% - var(--container-center-offset)) 0 auto;

--container-line-inset: var(--container-line-pos-bottom);
      --container-line-width: var(--container-line-length);
      --container-line-height: var(--container-line-thickness);
    }

:has(#theme-Container-Tab-Tweaks[uc-container-tweaks-pins="expanded"])
      #vertical-pinned-tabs-container {
      --container-line-length: var(--container-underline-length);
      --container-center-offset: calc(var(--container-line-length) / 2);
      --container-line-pos-bottom: auto
        calc(50% - var(--container-center-offset)) 0 auto;

--container-line-inset: var(--container-line-pos-bottom);
      --container-line-width: var(--container-line-length);
      --container-line-height: var(--container-line-thickness);
    }
  }
}