Small caps, warm ground, one loud red.
A warm institutional system built on three unusual choices: every heading is set in a true small-caps cut, the default page ground is cream rather than white, and the primary action is a solid crimson block with a hairline white keyline set inside it.
Headings use a real small-caps cut, not faked capitals. It reads as formal without reading as loud, which is what lets a 40px heading sit calmly above 16px body copy instead of overwhelming it.
The most common surface on the site is a warm cream, not white. White is what you switch to for contrast. Getting this the right way round is most of the difference between this system and a generic one.
A crimson block with a 1px white border and a 4px crimson outline outside it, so a thin white rule floats inside the colour. It is the single most recognisable component here; do not simplify it to a plain fill.
The typefaces are open substitutes for licensed ones — Spectral SC and Spectral for Le Monde Livre Classic, Mulish for Proxima Nova. And Bordeaux is an added error colour: the site’s own error style sets error text to the brand crimson, which makes a failed form look exactly like a call to action. Both are marked in the README.