body{
        width: 800px;
        width: 90%;
        margin-left: auto;
        margin-right: auto;
}
@media (min-width: 640px){
    html{
        background-color:#eaf6ff;
        font-size: 2.5rem;
    }
}
h1 {
    font-size: 1.5rem;
}
#fixed-size-grid-items aside {
    width: 170px;
    margin: 10px;
}

#fixed-size-grid-items li {
    list-style: none;
    display: inline-flex;
    flex-wrap: wrap;
}

#stretchable-grid-items li {
    width: 100%;
    list-style: none;
    display: inline-flex;
}

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

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

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

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