body{
    width: min(800px, 90%); 
    margin: 0 auto;  
}

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

@media(max-width: 499px){
    h1{
        font-size: 1.5rem;
    }
}

#fixed-size-grid-items aside{
    width: 170px;
    margin: 10px;
    font-size: 0.8rem;
}

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

#fixed-size-grid-items li{
    list-style: none;
    box-sizing: border-box;
}

#stretchable-grid-items ul{
    display: flex;
    flex-wrap: wrap;
    margin: 1rem -10px;  
    padding: 0;
}

#stretchable-grid-items li{
    width: 100%;
    list-style: none;
    box-sizing: border-box;
}
    
#stretchable-grid-items aside{
    margin: 10px;
}

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

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