Build it

Centre the hero card — in a container that runs downwards

EasyMain axis vs cross axis

The same justify-content: center that centred the masthead brand horizontally sent this card sliding down the middle of the hero instead. Nothing about the CSS changed. The container did.

.hero is already a flex container running as a column. Centre .card HORIZONTALLY inside it and leave it flush with the top. Keep the hero a column.

Hint

In a column, which axis are the items laid out along — and therefore which property is now the horizontal one?

Live preview1000×700

Your stylesheet

checked in a real browser, four ways

The fixture — markup and base stylesheet

You cannot change either of these. They are what your selectors have to reach, and they are the same ones the judge renders.

<section class="hero"><div class="card"></div></section>

*, *::before, *::after { box-sizing: border-box; }
html, body { margin: 0; padding: 0; }
body { background: #0b0b0f; color: #e8e8ef; font: 16px/1.4 system-ui, -apple-system, sans-serif; }
.hero { width: 420px; height: 560px; background: #16161d; display: flex; flex-direction: column; }
.card { width: 220px; height: 140px; background: #ffd166; }