body {
  font-family: Tahoma, Verdana, sans-serif;
  margin-left: 40px;
}
h1,h2,h3 {
  font-family: Tahoma, Verdana, sans-serif;
}
p {
  font-family: Tahoma, Verdana, sans-serif;
}


.header {
  background-color: #f1f1f1;
  padding: 10px;
  text-align: left;
}

.topnav {
  overflow: hidden;
  background-color: #00aa00;
}

.topnav a {
  float: right;
  display: block;
  color: white;
  text-align: center;
  padding: 14px 16px;
  text-decoration: none;
}

.topnav a:hover {
  background-color: #33dd33;
  color: white;
}

.button a {
  background-color: #00aa00;
  color: white;
  padding: 14px 16px;
}




.column {
  float: left;
  width: 33.33%;
  padding: 15px;
}

.row::after {
  content: "";
  display: table;
  clear: both;
}

@media screen and (max-width:600px) {
  .column {
    width: 100%;
  }
}