/* Navigation shared by the four course topics. */
header{flex-wrap:wrap;gap:12px}header .logo{min-width:0}header nav{flex-wrap:wrap;max-width:100%}
@media(max-width:900px){header{position:static;padding:16px}header nav{gap:4px}header nav .nav-link{font-size:.85rem;padding:6px 8px}}
@media(max-width:500px){header .logo{font-size:1rem}.cards-grid{grid-template-columns:minmax(0,1fr)}.hero h1{font-size:1.9rem;overflow-wrap:anywhere}.hero-pill{max-width:100%}}