<div class="letter-box">
<div class="letter-border">
</div>
</div>
.letter-border {
width: 100%;
height: 100%;
background: #fbfaf5;
}
.letter-box {
width: 278px;
height: 176px;
padding: 5px;
box-sizing: border-box;
background: linear-gradient(
45deg,
#f25953 12.5%,
#fbfaf5 12.5%, #fbfaf5 25%,
#5590d6 25%,#5590d6 37.5%,
#fbfaf5 37.5%,#fbfaf5 50%,
#f25953 50%,#f25953 62.5%,
#fbfaf5 62.5%, #fbfaf5 75%,
#5590d6 75%, #5590d6 87.5%,
#fbfaf5 87.5%, #fbfaf5 100%
);
background-size: 70px 70px;
}