So after doing a dozen blog upgrades from Ghost v3 to Ghost v4/Casper v4, this worked best overall:
<style type='text/css'>
/* Hide the Membership/Subscribe subsystem */
a.gh-head-button,
#ghost-portal-root,
.footer-cta,
.gh-head-actions,
.site-footer a[href^="https://ghost.org"] { display: none; }
.gh-head-inner { grid-template-columns: auto auto; }
.gh-head-brand { max-width: 400px; }
.site-footer-nav ul, .gh-head-menu { justify-content: flex-end; }
/* make serif Article font match sans-serif index page font */
/* Set font-family on body if you want to tweak it. */
article.post p {
font-family: inherit;
}
</style>