* {
  box-sizing: border-box;
}

body {
  font-family: Arial, Helvetica, sans-serif;
  margin: 0;
}

header {
  padding: 10px;
  text-align: center;
  background: #1abc9c;
  color: white;
}

header h1 {
  font-size: 40px;
}

nav {
  overflow: hidden;
  background-color: #333;
  position: sticky;
  position: -webkit-sticky;
  top: 0;
}


nav a {
  float: left;
  display: block;
  color: white;
  text-align: center;
  padding: 14px 20px;
  text-decoration: none;
}



nav a.right {
  float: right;
}


nav a:hover {
  background-color: #ddd;
  color: black;
}


nav a.active {
  background-color: #666;
  color: white;
}


.row {  
  display: -ms-flexbox; 
  display: flex;
  -ms-flex-wrap: wrap; 
  flex-wrap: wrap;
}

aside {
  -ms-flex: 30%; 
  flex: 30%;
  background-color: #f1f1f1;
  padding: 20px;
}


main {   
  -ms-flex: 70%; 
  flex: 70%;
  background-color: white;
  padding: 20px;
}

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

iframe {
  width: 100%;
  max-width: 560px;
  height: 315px;
  display: block;
  margin-bottom: 10px;
}

.videorow1, .videorow2 {
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
}

footer {
  padding: 20px;
  text-align: center;
}

/* Responsive layout - when the screen is less than 700px wide, make the two columns stack on top of each other instead of next to each other */
@media screen and (max-width: 700px) {
  .row {   
    flex-direction: column;
  }
}

/* Responsive layout - when the screen is less than 400px wide, make the navigation links stack on top of each other instead of next to each other */
@media screen and (max-width: 400px) {
  nav a {
    float: none;
    width: 100%;
  }
}