My minimal, gruvbox inspired Firefox customization

userChrome.css

/* Check out https://www.reddit.com/r/FirefoxCSS/ for an explanation on how to customize */
/* This hides a ton of buttons because I use Vimium for most navigation */
/* Screenshot at https://feed.grantcuster.com/post/1596224341/ */

:root {
  --base00: #282828;
  --base01: #3c3836;
  --base02: #504945;
  --base04: #bdae93;
  --base05: #d5c4a1;
  --base06: #ebdbb2;
}

#navigator-toolbox #toolbar-menubar, 
#navigator-toolbox #back-button, 
#navigator-toolbox #forward-button,
#navigator-toolbox .tab-close-button,
#navigator-toolbox #tabs-newtab-button,
#navigator-toolbox #tracking-protection-icon-container,
#navigator-toolbox #pageActionSeparator,
#navigator-toolbox #pageActionButton,
#navigator-toolbox #identity-box
{
  display: none;
}

#navigator-toolbox {
  font-family: 'JetBrains Mono' !important;
  font-size: 13.33px;
  line-height: 16px;
  border-bottom: none !important;
}

/* url bar */
#navigator-toolbox toolbarspring {
  display: none;
}
#navigator-toolbox .tab-line {
  display: none;
}
#navigator-toolbox #urlbar-container {
  padding: 0 !important;
  margin: 0 !important;
}
#navigator-toolbox #urlbar {
  border: none !important;
  border-radius: 0 !important;
  box-shadow: none !important;
}
#navigator-toolbox #urlbar-background {
  background: var(--) !important;
  border: none !important;
  margin: 0 !important;
  padding: 0 !important;
}
#navigator-toolbox #urlbar {
  background: var(--base00) !important;
  color: var(--base06) !important;
  padding: 0 !important;
  padding-left: 6px !important;
}
#navigator-toolbox #tracking-protection-icon-container {
  display: none;
}
#navigator-toolbox #urlbar-zoom-button {
  border: none !important;
}

/* buttons */
#navigator-toolbox #PanelUI-button {
  border: none !important;
}
#navigator-toolbox #nav-bar {
  background: var(--base00) !important;
}
#navigator-toolbox .toolbarbutton-1 {
  background: pink;
  width: 26px;
  background: var(--base01);
  border-left: solid 1px var(--base00);
  box-shadow: none !important;
}
#navigator-toolbox #PanelUI-menu-button {
  background: var(--base00);
  border: none;
}
#navigator-toolbox toolbarbutton image {
  display: none;
}
#navigator-toolbox #PanelUI-menu-button image {
  display: block;
}

/* tabs */
#navigator-toolbox .tab-content {
  font-size: 12px;
  line-height: 14px;
  padding: 1px 4px 1px 5px !important;
}
#tabbrowser-tabs,
#tabbrowser-arrowscrollbox {
  min-height: 0 !important;
}
#navigator-toolbox .toolbar-items {
  background: var(--base01);
}
#navigator-toolbox .tab-background {
  background: var(--base01) !important;
  border: none !important;
  box-shadow: none !important;
  border: none !important;
}
#navigator-toolbox .tabbrowser-tab .tab-label {
  color: var(--base05) !important;
}
#navigator-toolbox .tab-background .tab-line {
  display: none;
}
#navigator-toolbox .tabbrowser-tab::after {
  display: none !important;
}
#navigator-toolbox .tab-icon-image {
  margin-top: 0 !important;
}

#navigator-toolbox .tab-background[selected='true'] {
  background: var(--base04) !important;
}
#navigator-toolbox .tabbrowser-tab[selected='true'] .tab-label {
  color: var(--base01) !important;
}


/* hide fullscreen toggle bar */
#fullscr-toggler {
  display: none;
}


/* hide tabs if only one */
#tabbrowser-tabs
  .tabbrowser-tab[first-visible-tab='true'][last-visible-tab='true'] {
  visibility: collapse !important;
}

/*** BEGIN Firefox 77 (June 2, 2020) Override URL bar enlargement ***/

  /* Compute new position, width, and padding */

  #urlbar[breakout][breakout-extend] {
    top: 5px !important;
    left: 0px !important;
    width: 100% !important;
    padding: 0px !important;
  }
  /* for alternate Density settings */
  [uidensity="compact"] #urlbar[breakout][breakout-extend] {
    top: 3px !important;
  }
  [uidensity="touch"] #urlbar[breakout][breakout-extend] {
    top: 4px !important;
  }

  /* Prevent shift of URL bar contents */

  #urlbar[breakout][breakout-extend] > #urlbar-input-container {
    height: var(--urlbar-height) !important;
    padding: 0 !important;
  }

  /* Do not animate */

  #urlbar[breakout][breakout-extend] > #urlbar-background {
    animation: none !important;;
  }

  /* Remove shadows */

  #urlbar[breakout][breakout-extend] > #urlbar-background {
    box-shadow: none !important;
  }

/*** END Firefox 77 (June 2, 2020) Override URL bar enlargement ***/