代码如下：

.grid{
    background:#ccc;
    background-image: linear-gradient(white 0px,transparent 0),
    linear-gradient(90deg, white 0px,transparent 0),
    linear-gradient(hsla(0,0%,100%,.3) 1px,transparent 0),
    linear-gradient(90deg,hsla(0,0%,100%,.3) 1px,transparent 0);
    background-size:75px 75px,75px 75px,15px 15px,15px 15px;
}

效果图：

CSS实现网格背景!-卖坚果的怪叔叔