$dark: #000;
$light: #FFF;

$size: 55px;

body {
  margin: 0;
  padding: 0;
}

.container {
  width: 100%;
  position: absolute;
  top: 0;
  bottom: 0;
  display: -webkit-flex;
  display: flex;
  align-items: center;
  justify-content: center;
}

.squares {
  width: 16*$size;
  height: 14*($size+4px);
  overflow: hidden;
}

.block, .block:after {
  width: $size;
  height: $size;
  background: $dark;
  padding-left: $size;
  content: "";
  float: left;
  position: relative;
}

.block:after {
  background: $light;
  position: absolute;
  left: $size;
  top: 0;
}

.row {
  border-top: 4px solid lighten($dark, 30%);
  height: $size;
  width: 150%;
  -webkit-animation: EXPAND 5s infinite;
  animation: EXPAND 5s infinite;
  -webkit-animation-delay: 5s;
  animation-delay: 5s;
}
.row:nth-last-child(1) {
  border-bottom: 4px solid lighten($dark, 30%);
}
.row:nth-child(2n) {
  padding-left: 0.6*$size;  
}

@-webkit-keyframes EXPAND {
  50% {
    padding-left: 0px;
  }
}

@keyframes EXPAND {
  50% {
    padding-left: 0px;
  }
}

@import url(http://fonts.lug.ustc.edu.cn/css?family=Open+Sans);
.caption {
  background: $light;
  color: $dark;
  position: absolute;
  top: 0px;
  left: 0px;
  z-index: 100;
  font-size: 2em;
  text-align: center;
  width: 100%;
  font-family: Open Sans, sans-serif;
}