sidebar.css

/* Hide splitter, when using Tree Style Tab. This rule removes the sidebar splitter when Tree Style Tab is active. */
#sidebar-box[sidebarcommand="treestyletab_piro_sakura_ne_jp-sidebar-action"] + #sidebar-splitter {
  display: none !important;
}

/* Hide sidebar header, when using Tree Style Tab. This rule hides the header of the sidebar when Tree Style Tab is active. */
#sidebar-box[sidebarcommand="treestyletab_piro_sakura_ne_jp-sidebar-action"] #sidebar-header {
  visibility: collapse;
}

/* Shrink sidebar until hovered, when using Tree Style Tab. */
:root {
  --thin-tab-width: 35px;
  --wide-tab-width: 250px;
}

#sidebar-box:not([sidebarcommand="treestyletab_piro_sakura_ne_jp-sidebar-action"]) {
  min-width: var(--wide-tab-width) !important;
  max-width: none !important;
}

#sidebar-box[sidebarcommand="treestyletab_piro_sakura_ne_jp-sidebar-action"] {
  position: relative !important;
  transition: all 100ms !important;
  min-width: var(--thin-tab-width) !important;
  max-width: var(--thin-tab-width) !important;
  z-index: calc(var(--browser-area-z-index-tabbox, 10000) + 1) !important;
}

#sidebar-box[sidebarcommand="treestyletab_piro_sakura_ne_jp-sidebar-action"]:hover {
  transition: all 200ms !important;
  min-width: var(--wide-tab-width) !important;
  max-width: var(--wide-tab-width) !important;
  margin-right: calc((var(--wide-tab-width) - var(--thin-tab-width)) * -1) !important;
}