Adaptative images in Harlowe

No question for that time, but a pair of CSS snippets that I founded usefull.

For the background :
I'have played around with big pictures as background for stories and finaly tried the css below. I'ts a little complicated but gives you a pretty background for most size of devices :

html {
background-image: url("./medias/fond_loup02nb-compressor.jpg");
background-size:cover;
background-repeat:no-repeat;
background-position:center center;
background-attachment: fixed;
}

and for ordinary images :
img {
display: block;
margin:0 0px;
margin-left: auto;
margin-right: auto;
padding-top:0.5rem;
max-width: 100%;
height:auto;
}

What do you mind ?