<button>X</button></x-cell>

            <x-cell><button>4</button></x-cell>
            <x-cell><button>5</button></x-cell>
            <x-cell><button>6</button></x-cell>
            <x-cell class="orange"><button>&mdash;</button></x-cell>

            <x-cell><button>1</button></x-cell>
            <x-cell><button>2</button></x-cell>
            <x-cell><button>3</button></x-cell>
            <x-cell class="orange"><button>+</button></x-cell>

            <x-cell span="1+2"><button>0</button></x-cell>
  