网格线

html,
body {
height: 100%;
}
body {
font-size:37.5px;
}
.error {
position: relative;
}
.error::before {
content: '';
position: absolute;
top:50%;
100%;
height: 6.25em;
background: linear-gradient(135deg, transparent, transparent 45%, red, transparent 55%, transparent 100%), linear-gradient(45deg, transparent, transparent 45%, blue, transparent 55%, transparent 100%);
background-size: 0.5em 0.5em;
}