body {
  width: 800px;
  margin: 0px auto;
}

@media (max-width: 800px) {
  body {
    width: 90%;
  }
}

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

  h1 {
    font-size: 2.5rem;
  }
}

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

#stretchable-grid-items 
ul {
  list-style-type: none;
  font-size: 0px;
  padding-left: 0px;
  margin: 1rem -10px;
}

#stretchable-grid-items 
li {
  display: inline-block;
  width: 100%;
  font-size: 0.8rem;
  vertical-align: top;
}

#stretchable-grid-items 
aside {
  margin: 10px;
}

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

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

#fixed-size-grid-items 
ul {
  list-style-type: none;
  padding-left: 0px;
}

#fixed-size-grid-items 
li {
  display: inline-block;
  font-size: 0.8rem;
  vertical-align: top;
}

#fixed-size-grid-items 
aside {
  width: 170px;
  margin: 10px;