godot/scene/theme/icons/region_unfolded.svg

<svg xmlns="http://www.w3.org/2000/svg" width="12" height="12"><path fill="#fff" d="M10 3a1 1 0 0 0-1-1H3a1 1 0 0 0-1 1v6a1 1 0 0 0 1 1h6a1 1 0 0 0 1-1zM3 5.75a1 1 0 0 1 1.414-1.414L6 5.922l1.586-1.586A1 1 0 0 1 9 5.75L6.707 8.043a1 1 0 0 1-1.414 0z"/></svg>