body{/*正三角形(大)を敷き詰めた背景*/
background-size:50px 86.6px;
background-color:pink;
background-image:
linear-gradient(-60deg,rgba(255,255,255,0.5) 25%, transparent 25%),
linear-gradient(60deg,rgba(255,255,255,0.5) 25%, transparent 25%),
linear-gradient(-60deg,rgba(255,255,255,0.5) 25%, transparent 25%),
linear-gradient(60deg,rgba(255,255,255,0.5) 25%, transparent 25%);
background-position:0 0,0 0,25px 43.3px,25px 43.3px;}