//svgを使う

  



.diagonal { position: absolute; top: 0; bottom: 0; left: 0; right: 0; }
.rightUp {
background-image: url('data:image/svg+xml;base64,PHN2ZyB4bWxucz0iaHR0cDovL3d3dy53My5vcmcvMjAwMC9zdmciIHN0eWxlPSJ3aWR0aDoxMDAlO2hlaWdodDoxMDAlOyI+PGxpbmUgeDE9IjEwMCUiIHkxPSIwJSIgeDI9IjAlIiB5Mj0iMTAwJSIgc3R5bGU9InN0cm9rZTogIzMzMzMzMztzdHJva2Utd2lkdGg6IDE7Ij48L2xpbmU+PC9zdmc+');
}
.leftUp {
background-image: url("data:image/svg+xml;base64,PHN2ZyB4bWxucz0iaHR0cDovL3d3dy53My5vcmcvMjAwMC9zdmciIHN0eWxlPSJ3aWR0aDoxMDAlO2hlaWdodDoxMDAlOyI+PGxpbmUgeDE9IjAlIiB5MT0iMCUiIHgyPSIxMDAlIiB5Mj0iMTAwJSIgc3R5bGU9InN0cm9rZTogIzMzMzMzMztzdHJva2Utd2lkdGg6IDE7Ij48L2xpbmU+PC9zdmc+");
}

//css のみ：鋭角で細くすると点線・ギザギザになってしまう。
//50%から同量あける
.leftUpp { background-image: linear-gradient(to top right,
                       transparent, transparent 48.7%,
                       #ccc 48.7%, #ccc 51.3%,
                       transparent 50.3%, transparent);
}