style.css

body {
  margin: 0;
  font-family: "Helvetica Neue", Helvetica, Arial, sans-serif;
  font-size: 14px;
  line-height: 1.42857143;
  color: #333;
}
.container {
  padding-right: 15px;
  padding-left: 15px;
  margin-right: auto;
  margin-left: auto;
}
h1 {
  font-size: 36px;
  margin-top: 20px;
  margin-bottom: 10px;
  font-family: inherit;
  font-weight: 500;
  line-height: 1.1;
  color: inherit;
}
p {
  margin: 0 0 10px;
}
code {
  padding: 2px 4px;
  font-size: 90%;
  color: #c7254e;
  background-color: #f9f2f4;
  border-radius: 4px;
  font-family: Menlo, Monaco, Consolas, "Courier New", monospace;
}
#box {
  display: flex;
  flex-flow: row wrap;
}
.square {
  height: 300px;
  width: 300px;
  font-size: 28px;
  display: flex;
  flex: 1 1 auto;
  justify-content: center;
  align-items: center;
}
a.dark {
  color: #333;
  text-decoration: none;
}
a.light {
  color: #EEE;
  text-decoration: none;
}
a.light:hover, a.dark:hover {
  text-decoration: underline;
}