/* 1. Body width management: 800px OR 90%, centered */
body {
  margin-left: auto;
  margin-right: auto;
  width: 90%;
  max-width: 800px;
}

/* 2. Background color at 640px and up */
@media (min-width: 640px) {
  body {
    background-color: #eaf6ff;
  }
}

/* 3. Headline size */
h1 {
  /* default size can be anything reasonable; overridden by media queries below */
  font-size: 2rem;
}

@media (max-width: 499px) {
  h1 {
    font-size: 1.5rem;
  }
}

@media (min-width: 640px) {
  h1 {
    font-size: 2.5rem;
  }
}

/* 4. Fixed-size grid items */
#fixed-size-grid-items ul.fixed-grid {
  list-style: none;
  padding-left: 0;
  margin: 0;
  display: flex;
  flex-wrap: wrap;
}

#fixed-size-grid-items ul.fixed-grid li {
  margin: 0;
}

#fixed-size-grid-items ul.fixed-grid aside {
  box-sizing: border-box;
  width: 170px;
  margin: 10px;
  font-size: 0.8rem;
}

/* 5. Stretchable grid items */
#stretchable-grid-items ul.stretch-grid {
  list-style: none;
  padding-left: 0;
  margin: 1rem -10px;
  display: flex;
  flex-wrap: wrap;
}

/* default: 1 across */
#stretchable-grid-items ul.stretch-grid li {
  box-sizing: border-box;
  width: 100%;
}

/* each li contains an aside with 10px margin */
#stretchable-grid-items ul.stretch-grid aside {
  margin: 10px;
  font-size: 0.8rem;
}

/* 2 across at >480px */
@media (min-width: 480px) {
  #stretchable-grid-items ul.stretch-grid li {
    width: 50%;
  }
}

/* 4 across at >640px */
@media (min-width: 640px) {
  #stretchable-grid-items ul.stretch-grid li {
    width: 25%;
  }
}