1.    Note that those elements only exist once the Details pane has been expanded:

$('.history-toggle-btn span[title="Expand"]', window.parent.document).click();

    I haven't yet found a way to force the Details pane to expand and then interact with the Action History without having to add arbitrary delays.

2.    .history-comment is styled in \Styles\cf.css. Or to handle it from within a form:

$('head', window.parent.document).append('\
    <style type="text/css">\
        .history-comment {\
            font-size:24px;\
            color:#0da88b !important;\
        }\
    </style>');