body{
    width: 90%;
    max-width: 800px;
    margin-left: auto;
    margin-right: auto;
}
@media(min-width:640px){
    body{background-color: #eaf6ff;}
}
@media(min-width:640px){
    h1{font-size: 2.5rem;}
}
#fixed-size-grid-items ul{
    list-style-type: none;
    margin: 10px;
    padding-left: 0;
    display: flex;
    flex-wrap: wrap;
}
aside{
    width: 170px;
    margin: 10px;
    font-size: 0.8rem;
}
#stretchable-grid-items li{
    width: 100%;

    }
    @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;
        width: 170px;
    }
#stretchable-grid-items ul{
    list-style-type: none;
    padding-left: 0;
    display: flex;
    margin: 1rem -10px;
    flex-wrap: wrap;
    font-size: 0.8rem;
}