560 bytes css grid.
<!DOCTYPE HTML><head><linkrel="stylesheet" href="mini.css"/></head><html><body><divclass="container"><divclass="r1 left">R1</div><divclass="r11 right">R11</div></div><divclass="container"><divclass="r2 left">R2</div><divclass="r10 right">R10</div></div></body></html>