system-uicons/src/images/icons/minimise.svg

<svg height="21" viewBox="0 0 21 21" width="21" xmlns="http://www.w3.org/2000/svg"><g fill="none" fill-rule="evenodd" stroke="currentColor" stroke-linecap="round" stroke-linejoin="round" transform="translate(3 3)"><path d="m5.5 14.5v-5h-5"/><path d="m14.5 9.5h-5v5"/><path d="m.5 5.5h5v-5"/><path d="m9.5.5v5h5"/></g></svg>