* { box-sizing: border-box; }

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

/* BANNER / HEADER */
#banner {
  text-align: center;
}

header {
  background-image: url('https://upload.wikimedia.org/wikipedia/commons/thumb/9/97/The_Earth_seen_from_Apollo_17.jpg/1280px-The_Earth_seen_from_Apollo_17.jpg');
  background-size: cover;
  background-repeat: no-repeat;
  background-position: center;
  padding: 30px;
  text-align: center;
  color: white;
  text-shadow: 2px 2px 6px black;
}

header h1 { font-size: 36px; margin: 0; color: white; }
header h2 { font-size: 18px; margin: 5px 0; color: #f0f0f0; }
header a { color: #aee8ff; text-decoration: none; }

/* NAV */
nav {
  background-color: #1a1a2e;
  overflow: hidden;
}

nav a {
  float: left;
  color: white;
  padding: 14px 20px;
  text-decoration: none;
  font-size: 16px;
}

nav a:hover {
  background-color: #e94560;
  color: white;
}

/* ROW LAYOUT */
.row {
  display: flex;
  flex-wrap: wrap;
}

aside {
  flex: 25%;
  background-color: #f1f1f1;
  padding: 20px;
}

aside h3 { color: #1a1a2e; }

aside a {
  display: block;
  color: #1a1a2e;
  padding: 8px 0;
  text-decoration: none;
  font-size: 15px;
  border-bottom: 1px solid #ccc;
}

aside a:hover { color: #e94560; }

main {
  flex: 75%;
  background-color: white;
  padding: 25px;
}

/* FOOTER */
footer {
  background-color: #1a1a2e;
  color: white;
  text-align: center;
  padding: 20px;
}

footer a { color: #aee8ff; }

/* RESPONSIVE */
@media screen and (max-width: 700px) {
  .row { flex-direction: column; }
  aside, main { flex: 100%; }
  nav a { float: none; width: 100%; }
}