body{/*格子の内側*/
background-color:#79b;
background-size:25px 25px;
background-image:
linear-gradient(0deg,#963 5px,transparent 0),
linear-gradient(90deg,#963 5px,transparent 5px,transparent 22px,#ddb 22px),
linear-gradient(0deg,#ddb 8px,transparent 0);
}