css绘制网格背景

background-image: linear-gradient(90deg, rgba(50, 0, 0, 0.05) 3%, rgba(0, 0, 0, 0) 3%), linear-gradient(360deg, rgba(50, 0, 0, 0.05) 3%, rgba(0, 0, 0, 0) 3%);
background-size: 20px 20px;
background-repeat: repeat;
background-position: center center;

/* 主要是前两个属性的设置 */