css

/**
 * Dynamic Horizontal Tabs Toolbar (with animations)
 * sidebar.verticalTabs: false (with native horizontal tabs)
 */
 #main-window #TabsToolbar > .toolbar-items {
  overflow: hidden;
  transition: height 0.3s 0.3s !important;
}
/* Default state: Set initial height to enable animation */
#main-window #TabsToolbar > .toolbar-items { height: 3em !important; }
#main-window[uidensity="touch"] #TabsToolbar > .toolbar-items { height: 3.35em !important; }
#main-window[uidensity="compact"] #TabsToolbar > .toolbar-items { height: 2.7em !important; }
/* Hidden state: Hide native tabs strip */
#main-window[titlepreface*="XXX"] #TabsToolbar > .toolbar-items { height: 0 !important; }
/* Hidden state: Fix z-index of active pinned tabs */
#main-window[titlepreface*="XXX"] #tabbrowser-tabs { z-index: 0 !important; }
/* Hidden state: Hide window buttons in tabs-toolbar */
#main-window[titlepreface*="XXX"] #TabsToolbar .titlebar-spacer,
#main-window[titlepreface*="XXX"] #TabsToolbar .titlebar-buttonbox-container {
  display: none !important;
}
/* [Optional] Uncomment block below to show window buttons in nav-bar (maybe, I didn't test it on non-linux-i3wm env) */
/* #main-window[titlepreface*="XXX"] #nav-bar > .titlebar-buttonbox-container,
#main-window[titlepreface*="XXX"] #nav-bar > .titlebar-buttonbox-container > .titlebar-buttonbox {
  display: flex !important;
} */
/* [Optional] Uncomment one of the line below if you need space near window buttons */
/* #main-window[titlepreface*="XXX"] #nav-bar > .titlebar-spacer[type="pre-tabs"] { display: flex !important; } */
/* #main-window[titlepreface*="XXX"] #nav-bar > .titlebar-spacer[type="post-tabs"] { display: flex !important; } */




:where(#main-window) #browser{
  --uc-sidebar-width: 35px;
  --uc-sidebar-hover-width: 310px; /*ширина открытия вкладок*/
}
#main-window[sizemode="fullscreen"] #browser{
  --uc-sidebar-width: 1px;
}
#sidebar-box{
  --uc-autohide-sidebar-delay: 100ms; /* Wait 0.1s before hiding sidebar */
  --uc-autohide-transition-duration: 115ms;
  --uc-autohide-transition-type: linear;
  --browser-area-z-index-sidebar: 3;
  position: relative;
  min-width: var(--uc-sidebar-width) !important;
  width: var(--uc-sidebar-width) !important;
  max-width: var(--uc-sidebar-width) !important;
  z-index: var(--browser-area-z-index-sidebar,3);
  background-color: inherit;
  /* This directionality flipper is played so that sidebar "grows" into the right direction */
  direction: ltr;
  &:is([positionend],[sidebar-positionend]):not(:-moz-locale-dir(rtl)){
    direction: rtl;
  }
  > :-moz-locale-dir(rtl){
    direction: rtl;
  }
}

#main-window[sizemode="fullscreen"] #browser{ --uc-sidebar-width: 1px; }

#sidebar-splitter{ display: none }

#sidebar-header{
  overflow: hidden;
  color: var(--chrome-color, inherit) !important;
  padding-inline: 0 !important;
}

#sidebar-header::before,
#sidebar-header::after{
  content: "";
  display: flex;
  padding-left: 8px;
}

#sidebar-header,
#sidebar{
  transition: min-width var(--uc-autohide-transition-duration) var(--uc-autohide-transition-type) var(--uc-autohide-sidebar-delay) !important;
  min-width: var(--uc-sidebar-width) !important;
  will-change: min-width;
}
#sidebar-box:hover > #sidebar-header,
#sidebar-box:hover > #sidebar{
  min-width: var(--uc-sidebar-hover-width) !important;
  transition-delay: 0ms !important;
}

.sidebar-panel{
  background-color: transparent !important;
  color: var(--newtab-text-primary-color) !important;
}

.sidebar-panel #search-box{
  -moz-appearance: none !important;
  background-color: rgba(249,249,250,0.1) !important;
  color: inherit !important;
}

/* Add sidebar divider and give it background */

#sidebar,
#sidebar-header{
  background-color: inherit !important;
  border-inline: 0.5px solid rgb(80,80,80);
  border-inline-width: 0px 0.5px;
}

#sidebar-box:not([positionend],[sidebar-positionend]) > :-moz-locale-dir(rtl),
#sidebar-box:is([positionend],[sidebar-positionend]) > *{
  border-inline-width: 1px 0px;
}
@media -moz-pref("sidebar.revamp") {
  #sidebar, #sidebar-header{ border-style: none }
  #sidebar-box{ padding: 0 !important; }
}
/* Move statuspanel to the other side when sidebar is hovered so it doesn't get covered by sidebar */

#sidebar-box:not([positionend],[sidebar-positionend]):hover ~ #appcontent #statuspanel{
  inset-inline: auto 0px !important;
}
#sidebar-box:not([positionend],[sidebar-positionend]):hover ~ #appcontent #statuspanel-label{
  margin-inline: 0px !important;
  border-left-style: solid !important;
}
@media -moz-pref("userchrome.autohide-sidebar.static-layout.enabled"){
  #sidebar-box{
    min-width: var(--uc-sidebar-width) !important;
    contain: size;
    box-shadow: var(--content-area-shadow);
  }
  :root:not([inDOMFullscreen]) #tabbrowser-tabbox:not([sidebar-positionend]){
    margin-inline: var(--uc-sidebar-width) 0;
  }
  #sidebar-box:not([sidebar-positionend]){
    position: absolute !important;
    height: 100%;
    overflow: hidden;
    transition: min-width var(--uc-autohide-transition-duration) var(--uc-autohide-transition-type) var(--uc-autohide-sidebar-delay) !important;
    &:hover{
      min-width: var(--uc-sidebar-hover-width) !important;
      transition-delay: 0ms !important;
    }
  }
  #sidebar,#sidebar-header{
    min-width: var(--uc-sidebar-hover-width) !important;
    will-change: unset !important;
  }
  #sidebar-box[sidebar-positionend] > :is(#sidebar-header,#sidebar){
    transform: translateX(calc(var(--uc-sidebar-hover-width) - var(--uc-sidebar-width)));
    transition-property: transform !important;
  }
  #sidebar-box[sidebar-positionend]:hover > :is(#sidebar-header,#sidebar){
      transform: translateX(0);
      transition-delay: 0ms !important;
    }
  }
}


/* Hide native tabs strip and window buttons in tabs-toolbar */
/* Убирает верхний хэдр от вайрфокса*/
#TabsToolbar {
  display: none;
}

#sidebar-header {
  display: none;
}




#sidebar-box #sidebar-header {
  overflow: hidden !important;
}
#sidebar-box,
#sidebar-box #sidebar {
  min-width: 30px !important;
  max-width: auto !important;
}


/* AUTOCLOSE */
#sidebar-box.no-autohide {
  min-width: var(--uc-sidebar-hover-width) !important;
  max-width: var(--uc-sidebar-hover-width) !important;
  transition: none !important;
}

#sidebar-box.no-autohide #sidebar,
#sidebar-box.no-autohide #sidebar-header {
  min-width: var(--uc-sidebar-hover-width) !important;
  max-width: var(--uc-sidebar-hover-width) !important;
  transition: none !important;
}

/* Стилизация кнопки боковой панели */
#sidebar-button {
  list-style-image: url("chrome://browser/skin/sidebars.svg") !important;
}

/* Стиль для кнопки, когда боковая панель зафиксирована */
#sidebar-button[checked="true"] {
  background-color: highlight !important;
  color: highlighttext !important;
}

/* Скрыть стандартную панель боковой панели */
#sidebar-switcher-target,
#sidebar-close {
  display: none !important;
}