:root {
  --hds-blue: #2457d6;
  --hds-blue-dark: #1d4ed8;
  --hds-sky: #0ea5e9;
  --hds-text: #162033;
  --hds-muted: #64748b;
  --hds-surface: #f8fafc;
  --hds-card: #ffffff;
  --hds-border: #e2e8f0;
  --hds-radius-card: 18px;
  --hds-container-max: 1120px;
}
* { box-sizing: border-box; }
body { margin: 0; font-family: system-ui, -apple-system, Segoe UI, sans-serif; color: var(--hds-text); background: var(--hds-surface); line-height: 1.55; }
a { color: var(--hds-blue); }
a:hover { color: var(--hds-blue-dark); }
.hds-container { width: min(var(--hds-container-max), calc(100% - 32px)); margin: 0 auto; }
.hds-site-header, .hds-site-footer { background: #fff; border-bottom: 1px solid var(--hds-border); padding: 18px 0; }
.hds-site-footer { border-top: 1px solid var(--hds-border); border-bottom: 0; margin-top: 48px; color: var(--hds-muted); }
.hds-cluster { display: flex; align-items: center; justify-content: space-between; gap: 16px; flex-wrap: wrap; }
.brand { font-weight: 800; text-decoration: none; color: var(--hds-text); }
.hds-site-nav { display: flex; gap: 18px; }
.hds-section { padding: 42px 0; }
.hds-hero { background: linear-gradient(135deg, #eff6ff, #f8fafc); }
.hds-eyebrow { color: var(--hds-blue); font-weight: 800; text-transform: uppercase; letter-spacing: .08em; }
.hds-grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(240px, 1fr)); gap: 22px; }
.hds-card { background: var(--hds-card); border: 1px solid var(--hds-border); border-radius: var(--hds-radius-card); padding: 24px; box-shadow: 0 12px 28px rgba(15, 23, 42, .06); }
.hds-button { display: inline-block; border: 0; background: var(--hds-blue); color: white; border-radius: 999px; padding: 10px 18px; font-weight: 700; cursor: pointer; text-decoration: none; }
.hds-button:hover { color: white; background: var(--hds-blue-dark); }
.hds-button-secondary { background: #e0f2fe; color: #075985; }
.hds-button-secondary:hover { background: #bae6fd; color: #0c4a6e; }
.pill { display: inline-block; border-radius: 999px; background: #e0f2fe; color: #075985; padding: 3px 10px; }
.lesson-card-description { color: var(--hds-muted); }
.lesson-grid { align-items: start; }
.lesson-subsection { padding: 28px 0 0; }
.control { display: grid; gap: 6px; margin: 16px 0; }
.control input, .control select { width: 100%; accent-color: var(--hds-blue); }
.lesson-canvas { width: 100%; max-width: 720px; min-height: 260px; border: 1px solid #cbd5e1; border-radius: 14px; background: #ffffff; display: block; }
.readout { color: var(--hds-muted); font-family: ui-monospace, SFMono-Regular, Menlo, monospace; }
.parameter-list { display: grid; gap: 14px; }
.parameter-row { border-left: 4px solid var(--hds-sky); background: #fff; padding: 14px 18px; border-radius: 12px; }
.parameter-row h3 { margin: 0 0 4px; }
.parameter-row h3 span { color: var(--hds-muted); font-size: .9em; font-weight: 600; }
.parameter-row p { margin: 0; color: var(--hds-muted); }
.experiment-list li { margin: 0 0 12px; }

/* Phase 3 interactive example styling: token-based HDS-inspired controls. */
:root {
  --hds-green: #16a34a;
  --hds-red: #ef4444;
  --hds-shadow-strong: 0 22px 55px rgba(15, 23, 42, .12);
  --hds-control-bg: #f1f5f9;
}
.lesson-root { margin-top: -12px; }
.lesson-grid { grid-template-columns: minmax(0, 1.7fr) minmax(280px, .9fr); }
.simulation-card { position: relative; overflow: hidden; box-shadow: var(--hds-shadow-strong); }
.simulation-card::before { content: ""; position: absolute; inset: 0 0 auto; height: 5px; background: linear-gradient(90deg, var(--hds-blue), var(--hds-sky), var(--hds-green)); }
.simulation-toolbar { display: flex; justify-content: space-between; align-items: center; gap: 12px; margin-bottom: 14px; flex-wrap: wrap; }
.simulation-status { color: #166534; background: #dcfce7; border-radius: 999px; padding: 3px 10px; font-weight: 800; font-size: .85rem; }
.controls-card h2 { margin-top: 0; }
.control { background: var(--hds-control-bg); border: 1px solid var(--hds-border); border-radius: 14px; padding: 14px; }
.control span:first-child { font-weight: 800; color: var(--hds-text); }
.control output { color: var(--hds-blue); font-family: ui-monospace, SFMono-Regular, Menlo, monospace; }
.control-unit { color: var(--hds-muted); font-weight: 700; font-size: .88rem; }
.control input[type="range"] { min-height: 30px; cursor: pointer; }
.control input[type="number"], .control select { border: 1px solid var(--hds-border); border-radius: 12px; padding: 10px 12px; background: white; }
.lesson-canvas { box-shadow: inset 0 0 0 1px rgba(36, 87, 214, .06); }
.readout { min-height: 3.5rem; background: #0f172a; color: #e0f2fe; border-radius: 14px; padding: 12px 14px; overflow-wrap: anywhere; }
.parameter-row { box-shadow: 0 8px 20px rgba(15, 23, 42, .05); }
.experiment-list { background: #fff; border: 1px solid var(--hds-border); border-radius: var(--hds-radius-card); padding: 22px 22px 22px 44px; }
@media (max-width: 820px) {
  .lesson-grid { grid-template-columns: 1fr; }
  .hds-section { padding: 30px 0; }
}