* {
	box-sizing: border-box;
	margin: 0;
	padding: 0;
}
body {
	background: #ccc;
	font: 16px arial, sans-serif;
}
.mask {
	position: absolute;
	top: 0;
	right: 0;
	bottom: 0;
	left: 0;
	width: 41em;
	height: 28.5em;
	margin: auto;
	border: 0.1875em solid #fff;
	background: #fff;
	overflow: hidden;
}
.inner {
	position: absolute;
	width: 46.875em;
	height: 31.25em;
	margin: -1.5625em;
}
.inner div {
	position: relative;
	float: left;
	width: 3.125em;
	height: 3.125em;
	border: 0.1875em solid #808080;
}

.inner div:nth-child(odd):before {
	content: '';
    width: 4em;
    height: 4em;
    border-top: 0.375em solid #808080; 
    position: absolute;
    transform: rotate(45deg);
    transform-origin: 0.25em 0;
}
.inner div:nth-child(even):after {
	content: '';
    width: 4em;
    height: 4em;
    border-top: 0.375em solid #808080; 
    position: absolute;
    transform: rotate(-45deg);
    transform-origin: 3.125em 1.525em;
}
.inner span {
	position: absolute;
	top: 2.5625em;
	left: 2.5625em;
	width: 0.75em;
	height: 0.75em;
	background: #000;
	border: 0.0625em solid #fff;
	border-radius: 50%;
	z-index: 1;
}