* {box-sizing: border-box;}

body { 
  margin: 0;
  font-family: Arial, Helvetica, sans-serif;
  background-color: rgb(255, 255, 255);
}

.header {
  overflow: hidden;
  background-color: #ffffff;
  padding: 20px 10px;
}

.header a {
  float: none;
  color: black;
  text-align: center;
  padding: 12px;
  text-decoration: none;
  font-size: 18px; 
  line-height: 25px;
  border-radius: 4px;
}

.header a.logo {
  font-size: 25px;
  font-weight: bold;
}

.header a:hover {
  background-color: #ffffff;
  color: black;
}

.header a.active {
  background-color: dodgerblue;
  color: white;
}

.header-right {
  float: right;
}

img {
  max-width: 100%;
  height: auto;
}

@media screen and (max-width: 500px) {
  .header a {
    float: none;
    display: block;
    text-align: left;
  }
  
  .header-right {
    float: none;
  }
}

  .row {
    display: flex;
  }
  
  .column {
    flex: 33.33%;
    padding: 5px;
  }

  .div{

    float: left;
    
    width: 300px;
    
    }