[Proton] button to tabs, sound icon, menu padding

userChrome.css

/** Add small space at the top */
.tab-stack {
  margin-top: 4px;
}

/** Make tabs looks like tabs not buttons */
/* attach tabs to the toolbar */
.tab-background {
  margin: 0px !important;
  border-bottom-left-radius: 0 !important;
  border-bottom-right-radius: 0 !important;
  border: 0 !important;
}
/* tab background with 2px line at the top */
.tab-background[selected] {
  background: linear-gradient(
    to bottom,
    rgb(64, 70, 168) 2px,
    var(--toolbar-bgcolor) 2px,
    var(--toolbar-bgcolor) 100%
  ) !important;
}

/** Move tab context line from top to bottom (multi container color line) */
.tab-context-line {
  margin-top: 26px !important;
  margin-left: 6px !important;
  margin-right: 6px !important;
}

/** Fix tab icon (sound icon was replacing site icon) */
/* Always show tab icon */
.tab-icon-image {
  opacity: 1 !important;
}
/* Move tab sound icon to the top left */
.tab-icon-overlay {
  /* top - left */
  top: -6px !important;
  inset-inline-end: 6px !important;
  border-width: 0px !important;
  width: 14px !important;
  height: 14px !important;
  background-size: 11px 11px !important;
  background-color: color-mix(in srgb, var(--toolbar-bgcolor) 85%, white) !important;
}
.tab-icon-overlay:hover {
  /* background */
  fill-opacity: 1 !important;
}

/** Remove tab close button */
/* No Tab ⨉ */
.tab-close-button {
  display: none;
}
/* Fix mask size */
.tabbrowser-tab {
  --tab-label-mask-size: 1em !important;
}

/** Fix menu monster padding */
/* context menu padding */
menupopup > menuitem,
menupopup > menu {
  padding-block: 0.15em !important;
}
/* menu item padding */
toolbarbutton {
  --arrowpanel-menuitem-border-radius: 0px;
  --arrowpanel-menuitem-padding: 2px 10px;
  --arrowpanel-menuitem-margin: 0px;
}

/** Menu top items border and padding */
/* context menu top left button padding */
menugroup > menuitem:first-child {
  padding-left: 10px;
}
/* context menu top right button padding */
menugroup > menuitem:last-child {
  padding-right: 10px;
}
/* context menu top buttons padding */
menugroup > menuitem {
  padding-top: 4px;
  padding-bottom: 4px;
}
menugroup > menuitem > hbox > image {
  border-radius: 6px !important;
}
.panel-header > .subviewbutton {
  border-radius: 6px !important;
}

/* disable #titlebar inactive effect */
#titlebar {
  opacity: 1. !important;
}

New revision : fix Sound icon image + remove inactive effect on