:root {
    --bg: #f4f7fb;
    --surface: #ffffff;
    --surface-2: #eef4ff;
    --text: #172033;
    --muted: #647089;
    --border: #dce3ef;
    --primary: #1769e0;
    --primary-dark: #0c4fae;
    --success: #117a50;
    --warning: #9a5b00;
    --danger: #b42318;
    --shadow: 0 10px 32px rgba(27, 42, 74, .08);
}
* { box-sizing: border-box; }
body { margin: 0; background: var(--bg); color: var(--text); font: 16px/1.6 system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif; }
a { color: var(--primary); text-decoration: none; }
a:hover { text-decoration: underline; }
.site-header { min-height: 72px; display: flex; align-items: center; justify-content: space-between; gap: 24px; padding: 12px max(24px, calc((100vw - 1180px)/2)); background: var(--surface); border-bottom: 1px solid var(--border); }
.brand { display: flex; align-items: center; gap: 12px; color: var(--text); }
.brand:hover { text-decoration: none; }
.brand-mark { display: grid; place-items: center; width: 42px; height: 42px; border-radius: 12px; background: linear-gradient(135deg, #1769e0, #7b3fe4); color: #fff; font-weight: 800; font-size: 22px; }
.brand strong, .brand small { display: block; }
.brand small { color: var(--muted); font-size: 12px; }
.site-header nav { display: flex; gap: 20px; }
.site-header nav a { color: var(--text); font-weight: 650; }
.container { width: min(1180px, calc(100% - 40px)); margin: 0 auto; padding: 44px 0 72px; }
.hero { display: grid; grid-template-columns: minmax(0, 1fr) 300px; gap: 34px; align-items: center; padding: 38px; border-radius: 24px; background: linear-gradient(135deg, #fff 0%, #edf4ff 100%); border: 1px solid var(--border); box-shadow: var(--shadow); }
.eyebrow { display: inline-block; color: var(--primary); font-size: 13px; font-weight: 800; letter-spacing: .08em; text-transform: uppercase; }
h1 { margin: 8px 0 14px; font-size: clamp(32px, 5vw, 52px); line-height: 1.08; letter-spacing: -.03em; }
h2 { margin: 0 0 10px; line-height: 1.25; }
h3 { margin-top: 24px; }
p { margin: 0 0 14px; }
.hero p, .lesson-header p { max-width: 760px; color: var(--muted); font-size: 18px; }
.hero-actions { display: flex; flex-wrap: wrap; gap: 12px; margin-top: 24px; }
.button { display: inline-flex; align-items: center; justify-content: center; min-height: 42px; padding: 9px 16px; border-radius: 10px; border: 1px solid transparent; font: inherit; font-weight: 750; cursor: pointer; }
.button:hover { text-decoration: none; }
.button.primary { background: var(--primary); color: #fff; }
.button.primary:hover { background: var(--primary-dark); }
.button.secondary { background: var(--surface); color: var(--text); border-color: var(--border); }
.progress-card { padding: 24px; background: rgba(255,255,255,.82); border: 1px solid var(--border); border-radius: 18px; }
.progress-card strong { font-size: 20px; }
.progress-track { height: 10px; margin: 16px 0 8px; border-radius: 999px; background: #dce6f5; overflow: hidden; }
.progress-track span { display: block; width: 0; height: 100%; background: var(--primary); transition: width .25s ease; }
.text-button { padding: 0; background: none; border: 0; color: var(--muted); text-decoration: underline; cursor: pointer; }
.notice { margin: 26px 0; padding: 18px 20px; background: #fff8e8; border: 1px solid #f0d999; border-radius: 14px; }
.notice p { margin: 4px 0 0; color: #6e5220; }
.exercise-grid { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 18px; }
.exercise-card { display: flex; flex-direction: column; min-height: 250px; padding: 24px; background: var(--surface); border: 1px solid var(--border); border-radius: 18px; box-shadow: 0 4px 18px rgba(27,42,74,.04); transition: transform .16s ease, box-shadow .16s ease; }
.exercise-card:hover { transform: translateY(-2px); box-shadow: var(--shadow); }
.exercise-card.completed { border-color: #78c5a6; background: #f7fffb; }
.card-topline, .card-footer, .panel-heading, .output-heading { display: flex; align-items: center; justify-content: space-between; gap: 14px; }
.number { font-size: 30px; font-weight: 850; color: #b2bfd2; }
.level { padding: 4px 9px; border-radius: 999px; background: var(--surface-2); color: var(--primary); font-size: 12px; font-weight: 800; }
.exercise-card h2 { font-size: 23px; }
.exercise-card p { color: var(--muted); }
.card-footer { margin-top: auto; padding-top: 20px; border-top: 1px solid var(--border); }
.completion-label { color: var(--muted); font-size: 13px; font-weight: 700; }
.exercise-card.completed .completion-label { color: var(--success); }
.breadcrumb { display: flex; gap: 10px; color: var(--muted); margin-bottom: 22px; }
.lesson-header { display: flex; justify-content: space-between; align-items: flex-start; gap: 28px; margin-bottom: 28px; }
.lesson-header h1 { font-size: clamp(34px, 5vw, 48px); }
.lesson-layout { display: grid; grid-template-columns: minmax(0, 1fr) 310px; gap: 24px; align-items: start; }
.lesson-main, .lesson-sidebar { display: grid; gap: 20px; }
.panel { padding: 26px; background: var(--surface); border: 1px solid var(--border); border-radius: 18px; box-shadow: 0 4px 18px rgba(27,42,74,.04); }
.panel.compact { padding: 22px; }
.steps { padding-left: 24px; }
.steps li { margin: 10px 0; padding-left: 6px; }
.method { display: inline-block; padding: 3px 8px; border-radius: 6px; font-size: 12px; font-weight: 900; letter-spacing: .05em; }
.method.get { background: #e7f2ff; color: #0759ad; }
.method.post { background: #e8f8ef; color: #086c43; }
.method.download { background: #f0eaff; color: #6331a8; }
.panel-heading h2 { margin-top: 5px; }
.endpoint-row { display: flex; gap: 10px; align-items: stretch; margin: 18px 0; }
.endpoint-row code { flex: 1; padding: 13px 14px; overflow-x: auto; border: 1px solid var(--border); border-radius: 9px; background: #f7f9fc; white-space: nowrap; }
.copy-button, .key-box button { padding: 8px 12px; border: 1px solid var(--border); border-radius: 9px; background: #fff; cursor: pointer; }
pre { overflow: auto; margin: 12px 0 0; padding: 16px; border-radius: 12px; background: #111827; color: #e6edf7; font-size: 13px; }
.key-box { padding: 16px; border-radius: 12px; background: #fff8e8; border: 1px solid #efd596; }
.key-box label { display: block; margin-bottom: 8px; font-weight: 750; }
.key-box div { display: flex; gap: 8px; }
.key-box input { flex: 1; min-width: 0; padding: 9px 11px; border: 1px solid var(--border); border-radius: 8px; }
.key-box small { display: block; margin-top: 7px; color: var(--muted); }
.api-output { margin-top: 18px; }
.status-pill { padding: 3px 8px; border-radius: 999px; background: #e9eef6; font-size: 12px; font-weight: 800; }
.status-pill.ok { background: #e6f7ef; color: var(--success); }
.status-pill.error { background: #ffebe9; color: var(--danger); }
.success-panel { border-left: 5px solid var(--success); }
.lesson-nav { display: flex; justify-content: space-between; }
.site-footer { padding: 28px 20px; text-align: center; color: var(--muted); border-top: 1px solid var(--border); background: var(--surface); }
@media (max-width: 850px) {
    .hero, .lesson-layout { grid-template-columns: 1fr; }
    .exercise-grid { grid-template-columns: 1fr; }
    .site-header { align-items: flex-start; }
    .site-header nav { display: none; }
    .lesson-header { flex-direction: column; }
}
@media (max-width: 540px) {
    .container { width: min(100% - 24px, 1180px); padding-top: 24px; }
    .hero, .panel, .exercise-card { padding: 20px; }
    .endpoint-row, .key-box div { flex-direction: column; }
}
.pipeline { display: flex; flex-wrap: wrap; align-items: center; justify-content: center; gap: 10px; margin: 24px 0; padding: 16px 20px; background: var(--surface); border: 1px solid var(--border); border-radius: 14px; box-shadow: 0 4px 18px rgba(27,42,74,.04); }
.pipeline span { padding: 7px 11px; border-radius: 999px; background: var(--surface-2); color: var(--primary-dark); font-weight: 750; }
.pipeline b { color: var(--muted); }
.purpose-strip { margin-bottom: 24px; padding: 18px 22px; border-radius: 14px; background: #eef7ff; border: 1px solid #bdd9f7; }
.purpose-strip p { margin: 4px 0 0; color: #344865; }
.mapping-panel { border-top: 4px solid var(--primary); }
.production-panel { border-top: 4px solid var(--warning); }
.production-panel p { color: var(--muted); }
.big-picture-panel { margin-bottom: 24px; border-left: 5px solid #7b3fe4; background: linear-gradient(135deg, #fff, #f7f2ff); }
.big-picture-panel p { max-width: 900px; color: #3e4560; font-size: 17px; }
.concept-list { display: grid; gap: 10px; margin: 14px 0 0; padding-left: 22px; }
.guided-steps { display: grid; gap: 16px; margin-top: 20px; }
.guided-step { display: grid; grid-template-columns: 44px minmax(0, 1fr); gap: 16px; padding: 18px; border: 1px solid var(--border); border-radius: 14px; background: #fbfcff; }
.guided-step h3 { margin: 0 0 10px; font-size: 18px; }
.step-number { display: grid; place-items: center; width: 38px; height: 38px; border-radius: 50%; background: var(--primary); color: white; font-weight: 850; }
.guided-step dl { display: grid; gap: 8px; margin: 0; }
.guided-step dl div { display: grid; grid-template-columns: 180px minmax(0, 1fr); gap: 12px; }
.guided-step dt { font-weight: 800; color: var(--primary-dark); }
.guided-step dd { margin: 0; color: #46516a; }
.risk-panel { border-left: 5px solid var(--danger); background: #fff8f7; }
.risk-panel p { color: #673832; }
.reflection-panel { border-left: 5px solid #7b3fe4; }
.reflection-panel > p { color: var(--muted); }
.reflection-panel li { margin: 10px 0; }
.api-explanation { color: var(--muted); }
@media (max-width: 650px) {
    .guided-step { grid-template-columns: 1fr; }
    .guided-step dl div { grid-template-columns: 1fr; gap: 2px; }
}