userChrome.css

/*
 -- Colors --
*/

:root {
  --sfwindow: #11111b;
  --sfsecondary: #24273a;

  /* Window colors  */
  --toolbar-bgcolor: var(--sfsecondary) !important;
  --lwt-sidebar-background-color: var(--sfwindow) !important;
}

/*
 -- Tabs --
*/

#tabbrowser-tabs:not([movingtab])
  > #tabbrowser-arrowscrollbox
  > .tabbrowser-tab
  > .tab-stack
  > .tab-background[multiselected="true"],
#tabbrowser-tabs:not([movingtab])
  > #tabbrowser-arrowscrollbox
  > .tabbrowser-tab
  > .tab-stack
  > .tab-background[selected="true"] {
  background-image: none !important;
  background-color: var(--toolbar-bgcolor) !important;
}

/* Inactive tabs color */
#navigator-toolbox {
  background-color: var(--sfwindow) !important;
  border: none !important;
}

/* Favicon of new page */
.tab-icon-image[src="chrome://branding/content/icon32.png"]
{
  content: url("icons/foxlogo.svg") !important;
}

/* Disable shadows of the tabs */
.tabbrowser-tab:is([visuallyselected="true"], [multiselected])
  > .tab-stack
  > .tab-background {
  box-shadow: none !important;
}

/* Style tabs */
.tab-label {
  text-shadow: none !important;
  font-family: CaskaydiaCove Nerd Font;
  font-style: unset;
  font-size: small;
}

/* Disbale tabs borders */
.tab-background {
  border-radius: 0 0 !important;
  margin: 0px !important;
}

/*
-- Url --
*/

/* Center URL text */
#urlbar .urlbar-input-box {
  text-align: center !important;
}

#urlbar-input-container {
  background-color: var(--sfwindow) !important;
  border: 1px solid rgba(0, 0, 0, 0) !important;
}

#urlbar-container {
  margin-left: 0 !important;
}

#urlbar[focused="true"] > #urlbar-background {
  box-shadow: none !important;
}

/* Remove url bar panel */
.urlbarView {
  display: none !important;
}

/* Remove placeholder */
#urlbar-input::placeholder,
.searchbar-textbox::placeholder {
  opacity: 0 !important;
}

/* Change URL font */
#urlbar,
#searchbar .searchbar-textbox {
  font-family: CaskaydiaCove Nerd Font !important;
}

/* 
-- Arrow icons --
*/

#back-button image {
  list-style-image: url("icons/back.svg") !important;
}

#back-button:hover image {
  background: none !important;
}

/* forward - go button */
#forward-button image {
  list-style-image: url("icons/forward.svg") !important;
}

#forward-button:hover image {
  background: none !important;
}