body {
  margin: auto;
  width: 90%;
  max-width: 800px;
}

@media (min-width: 640px) {
  html {
    background-color: #eaf6ff;
  }

  h1 {
    font-size: 2.5rem;
  }
}

@media (max-width: 500px) {
  h1 {
    font-size: 1.5rem;
  }
}

ul{
  display: flex;
  flex-flow: row wrap;
  justify-content: center;
  padding: 0;
  list-style: none;
  margin: 1rem -10px 1rem -10px;
}

aside {
  margin: 10px;
  font-size: 0.8rem;
}

#fixed-size-grid-items aside {
  width: 170px;
}

@media (max-width: 640px) {
  #stretchable-grid-items li {
    width: 25%;
  }
}

@media (max-width: 480px) {
  #stretchable-grid-items li {
    width: 50%;
  }
}