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

/* when viewport width is above 640px */
@media (min-width: 640px) {
    body {
      background-color: #eaf6ff;
    }
    h1{
      font-size: 2.5rem;
    }
}

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

#fixed-size-grid-items ul{
  display: grid;
  grid-template-columns: 1fr 1fr 1fr 1fr;
  padding: 0;
}

/* grid of boxes that wraps horizontally */
#fixed-size-grid-items aside {
  width: 170px;
  margin: 10px;
  font-size: 0.8rem;
}

ul {
  list-style-type: none;
  padding-left: none;
}

#stretchable-grid-items ul{
  display: flex;
  flex-wrap: wrap;
  padding: 0;
  margin-left: -10px;
  margin-right: -10px;
  margin-top: 1rem;
  margin-bottom: 1rem;
}

/* small width: one across */
#stretchable-grid-items li{
  width: 100%;
  display: block;
}

/* when viewpower width is greater than 480px */
/* medium widths: 2-across */
@media(min-width:480px){
  #stretchable-grid-items li{
    width: 50%;
  }
}

/* small widths: 4-across */
@media(min-width:640px){
  #stretchable-grid-items li{
    width: 25%;
  }
}

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