Genuine small caps aren’t just scaled versions of normal caps, they’re completely different glyphs. Here’s a black uppercase ‘M’ in Arno Pro overlaid with a semi-transparent blue small-caps ‘M’. The blue letter has been scaled up (keeping the width and height ratio constant) so its height matches the conventional uppercase black glyph. You can see that small caps are wider and have thicker strokes and more sturdy serifs.

In CSS we can supposedly achieve this by setting font-variant: small-caps; but browser support is limited: all you’ll get are small versions of the uppercase glyphs. Instead I prefer to use font-feature-settings:'smcp'; Here’s a quick demo. The blue letters are, again, lowercase characters rendered as small caps and scaled to match the height of the conventional uppercase black glyph.