body {
    width: 90%;
    max-width: 800px;
    margin-left: auto; 
    margin-right: auto;
}
@media (min-width: 480px) {
    #stretchable-grid-items li {
        width: 50%;
        grid-template-columns: 1fr 1fr;
    }
}
@media (min-width: 640px) {
    body {
        background-color: #eaf6ff;
    }
    h1 {
        font-size: 2.5rem;
    }
    #stretchable-grid-items li {
        width:25%;
    }

}
@media (max-width: 500px) {
    h1 {
        font-size: 1.5rem;
    }
}
#fixed-size-grid-items ul{
    list-style: none;
    padding-left: 0;
}
#fixed-size-grid-items li {
    display: inline-flex;
    font-size: 0.8rem;
}
#fixed-size-grid-items aside {
    width: 170px;
    margin: 10px;
}
#stretchable-grid-items ul {
    list-style: none;
    padding: 0;
    display: inline-grid;
    grid-gap: 10px;
    margin: 1rem, -10px, 1rem, -10px;
}

#stretchable-grid-items li {
    width: 100%;
}
#stretchable-grid-items aside {
    margin:10px;
}

@media (min-width: 480px) {
    #stretchable-grid-items ul {
        grid-template-columns: 1fr 1fr;
    }
}

@media (min-width: 640px) {
    #stretchable-grid-items ul {
        grid-template-columns: 1fr 1fr 1fr 1fr;
    }
}