The font shorthand, as in font: italic 600 1rem/1.5 Georgia, serif, resets every longhand you omit. End font-family with a generic family such as serif, sans-serif, monospace, math or system-ui (the operating system's interface font). font-weight accepts 1 to 1000 (400 normal, 700 bold), font-synthesis decides whether the browser may fake a missing bold or italic, and font-size-adjust (Baseline 2024) scales fallback fonts to the same x-height so text does not jump when a web font arrives.
The font-variant-* longhands switch on optional OpenType glyphs: -caps (small-caps, all-small-caps), -numeric (oldstyle-nums, tabular-nums, diagonal-fractions, slashed-zero), -ligatures and -alternates. The low-level font-feature-settings: "smcp", "tnum" reaches features by four-letter tag; keep it for features that have no property.
<link rel="stylesheet" href="https://fonts.googleapis.com/css2?family=EB+Garamond">
<style>
body { font: 21px/1.45 "EB Garamond", Georgia, serif; margin: 8px; }
.sc { font-variant-caps: all-small-caps; letter-spacing: .05em; }
.frac { font-variant-numeric: diagonal-fractions; } .nolig { font-variant-ligatures: none; }
</style>
<div><span class="sc">NASA and HTML</span> in small caps, <span class="frac">3/4</span> cup</div>
<div>Ligatures on: fifty office files · off: <span class="nolig">fifty office files</span></div>