body{
    width: 800px;
    max-width: 90%;
    margin-left: auto;
    margin-right: auto;
}
@media (max-width: 640px){
    html{
        background-color: #eaf6ff ;
    }
    h1{
        font-size: 1.5rem;
    }
}
@media (min-width: 500px){
    h1{
        font-size: 2.5rem;
    }

}
#fixed-size-grid-items aside{
    width: 170px;
    margin: 10px;
    font-size: .8rem;
}

#fixed-size-grid-items ul{
    display:flex;
    flex-wrap: wrap;
    list-style: none;
    padding-left: 0;
}


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

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

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

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