/* for First Tab Space */
:root {
  --space-left-tabbar: 8px; /* If the option is not specified, it is equivalent to 0px. */
}

:root:not([tabsintitlebar]) #tabbrowser-tabs:not([positionpinnedtabs]),
:root:is([sizemode="maximized"], [sizemode="fullscreen"]) #tabbrowser-tabs:not([positionpinnedtabs]) {
  padding-inline-start: var(--space-left-tabbar) !important;
}