* {
  box-sizing: border-box;
}

body {
  margin: 0;
  background-color: #FFFFFF;
}

code {
  font-size: 110%;
  background-color: #F0FFF8;
}

pre {
  border: 1px solid #A0D0D0;
  background-color: #F0FFF8;
  padding: 4px 4px;
}

.header {
  background-color: #F0FFF8;
  padding: 8px;
  text-align: center;
}

.topnav {
  overflow: hidden;
  background-color: green;
}

/* topnav links */
.topnav a {
  float: left;
  display: block;
  color: #f2f2f2;
  text-align: center;
  padding: 8px 8px;
  text-decoration: none;
}

/* topnav color on hover */
.topnav a:hover {
  background-color: #20D020;
  color: black;
}

table, th, td {
  border: 2px solid gray;
  border-collapse: collapse;
}

/* Columns that float next to each other */
.column50 {
  float: left;
  width: 50%;
  padding: 15px;
}

/* Clear floats after the columns */
.row:after {
  content: "";
  display: table;
  clear: both;
}

/* Responsive layout - columns stack on top of each other */
@media (max-width:720px) {
  .column50 {
    width: 100%;
  }
}