Center the Talkyard Commentbox

This works for me:

.talkyard-comments {
    max-width: 750px;   /* you can change this */
    width: calc(100% - 40px);  /* 20 px whitespace on each side, on small screeens */
    margin-left: auto;
    margin-right: auto;
}

The reason this works is that now when the layout engine has to give the element a restricted width,
then, with margin-left and right = auto,
it'll add equally much whitespace to the left as to the right.

Even more details & ideas — one can use Flexbox too:

How to horizontally center a <div>?
https://stackoverflow.com/questions/114543/how-to-horizontally-center-a-div