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

html{
    @media (min-width: 640px){
        background-color: #eaf6ff;
    }
}

h1{
    @media (min-width: 640px){
        font-size:2.5rem;
    }
    @media (max-width: 500px){
        font-size:1.5rem;
    }
}

section#fixed-size-grid-items ul{
    display: flex;
    flex-wrap: wrap;
    padding-left: 0;
    width: 100%;
}
section#fixed-size-grid-items aside{
    width: 170px;
    margin: 10px;
    font-size: .8rem;
}
section#fixed-size-grid-items li{
    display: block;
}

section#stretchable-grid-items ul{
    display: flex;
    flex-wrap: wrap;
    padding-left: 0;
    width: 100%;
    margin-left: -10px;
    margin-right: -10px;
    margin-top: 1rem;
    margin-bottom: 1rem;

}
section#stretchable-grid-items aside{
    margin: 10px;
}
section#stretchable-grid-items li{
    display: block;
    width: 100%;
    @media (min-width: 480px){
        width: 50%;
    }
    @media (min-width: 640px){
        width: 25%;
    }
}