godot/editor/icons/GuiIndeterminateDisabled.svg

<svg xmlns="http://www.w3.org/2000/svg" width="16" height="16"><rect width="14" height="14" x="1" y="1" fill="gray" rx="2.33"/><path fill="#b3b3b3" d="M3 7h10v2H3z"/></svg>