message: change room header/timeline/composer bg
diff: // unified palette
  // try to use these colors when possible
  -$bg-color: #181b21;
  -$base-color: #15191E;
  +$bg-color: #15191E;
  +$base-color: $bg-color;
  $base-text-color: #ffffff;
  $header-panel-bg-color: #22262e;
  $header-panel-border-color: #000000;
  @@ -92,7 +92,7 @@ $settings-subsection-fg-color: $text-secondary-color;
  $topleftmenu-color: $text-primary-color;
  $roomheader-color: $text-primary-color;
  -$roomheader-bg-color: rgba(21, 25, 30, 0.6);
  +$roomheader-bg-color: $bg-color;
  $roomheader-addroom-bg-color: rgba(92, 100, 112, 0.3);
  $roomheader-addroom-fg-color: $text-primary-color;
  $tagpanel-button-color: $header-panel-text-primary-color;
  