:root {
  --zen-main-browser-background: light-dark(#ddd, #4a4a4a); 
  --zen-appcontent-separator-from-window: 20px;
}

html#main-window > body > toolbox#navigator-toolbox, 
hbox#browser {
  background: transparent !important;
} 

html#main-window > body {
  background: var(--zen-main-browser-background) !important;
}

#appcontent {
  border-radius: var(--zen-panel-radius);
  overflow: hidden;
  box-shadow: 0 4px 6px -1px rgb(0 0 0 / 0.1), 0 2px 4px -2px rgb(0 0 0 / 0.1);
  margin: var(--zen-appcontent-separator-from-window);
  margin-top: 0;
}