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



#fixed-size-grid-items ul{
    display:flex;
    flex-wrap:wrap;
    font-size:0.8rem;
    padding-left:0;
}

#fixed-size-grid-items li{
    display:block;
}

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

#stretchable-grid-items ul{
    display: flex;
    flex-wrap: wrap;
    font-size: 0.8rem;
    list-style:none;
    padding: 0;
    margin: 1rem -10px;
}

#stretchable-grid-items li{
    display: block;
    width: 100%;
}

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

@media(min-width: 640px) {
    body{
        background: #eaf6ff;
    }
    h1{
        font-size: 2.5rem;
    }
}

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

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

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