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

}

aside{
    width: 170px;
    margin: 10px;
    font-size: 0.8rem;
    display: block;

}
ul{
    display: flex;
    padding: 0;
    flex-wrap: wrap;
}
::marker{
    content: "";
}
#stretchable-grid-items li{
    width: 100%;
}
#stretchable-grid-items aside{
    margin: 10px;
}
#stretchable-grid-items ul{
    margin: 1rem -10px 1rem -10px;
}


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

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


@media (min-width: 640px) {
    body{background-color: #eaf6ff;}
    h1{font-size: 2.5rem;}
    #stretchable-grid-items li{width: 25%;}
  }