设置背景单元格

很简单~~~

body {
    background-image: linear-gradient(90deg,var(--linesColor) 3%,transparent 0),linear-gradient(0deg,var(--linesColor) 3%,transparent 0);
    background-position: 50%;
    background-size: 20px 20px;
    --linesColor: rgba(50,0,0,0.05);
}