SOURCE

body {
    background: #58a;
    background-image: linear-gradient(white 2px, transparent 0), linear-gradient(90deg, white 2px, 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;
}