body{
    width:min(800px,90%);
    text-align: center;
    margin-left:auto;
    margin-right:auto;
}
@media (min-width:640px){
html{
    background-color:#eaf6ff ;
}
h1{
    font-size:2.5rem;
}
}

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

section#fixed-size-grid-items ul{
    display:flex;
    flex-wrap: wrap;
    padding-left:0;
}
section#fixed-size-grid-items aside{
    width:170px;
    margin: 10px;
    font-size:0.8rem;
}
section#fixed-size-grid-items{
    display:block;
}
section#fixed-size-grid-items li{
    font-size:0;
}
section#stretchable-grid-items {
    display: block;
}
section#stretchable-grid-items ul {
    display:flex;
    flex-wrap: wrap;
    padding-left:0;
    margin-left:-10px;
    margin-right:-10px;
    margin-top:1rem;
    margin-bottom:1rem;

}
section#stretchable-grid-items li {
    width:100%;
    font-size:0;
}
section#stretchable-grid-items aside {
    margin:10px;
    font-size:0.8rem;
}
@media (min-width:480px){
    section#stretchable-grid-items li {
        width:50%;
}
}
@media (min-width:640px){
    section#stretchable-grid-items li {
        width:25%;
}
}