.lesson-intro{max-width:1040px;margin:auto;padding:28px 24px 64px;color:var(--ui-text)}.lesson-intro nav{font-size:13px;margin-bottom:24px}.lesson-intro a{color:var(--ui-accent)}.lesson-intro header{padding:30px;border:1px solid var(--ui-line);border-radius:14px;background:var(--ui-raised);margin-bottom:24px}.intro-eyebrow{font-size:11px;letter-spacing:1.4px;font-weight:700;color:var(--ui-muted)}.lesson-intro h1{font-size:30px;line-height:1.3;margin:12px 0}.lesson-intro p{font-size:15px;line-height:1.8;color:var(--ui-muted);margin:8px 0 0}.intro-rule-grid{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:18px}.intro-rule-grid>section,.intro-teacher-note,.intro-next{border:1px solid var(--ui-line);background:var(--ui-surface);border-radius:12px;padding:24px;min-width:0}.intro-number{display:grid;place-items:center;width:32px;height:32px;border-radius:8px;background:var(--ui-raised);color:var(--ui-accent);font-size:13px;font-weight:700}.lesson-intro h2{font-size:18px;line-height:1.4;margin:14px 0 0}.intro-teacher-note,.intro-next{margin-top:22px}.intro-teacher-note h2{margin-top:0}.intro-next label{display:flex;align-items:flex-start;gap:12px;font-size:15px;line-height:1.6}.intro-next input{width:20px;height:20px;flex-shrink:0;margin:2px 0;accent-color:var(--ui-accent)}.intro-next button{display:inline-flex;align-items:center;gap:16px;min-height:46px;padding:12px 18px;margin-top:22px;font:600 15px var(--font-ui);border:1px solid #245fbd;border-radius:8px;background:#245fbd;color:#fff;cursor:pointer}.intro-next button:hover{background:#184d9e}.intro-next>p{font-size:12px}#intro-error{color:var(--ui-danger);margin:0 0 16px}.lesson-intro :focus-visible{outline:3px solid var(--ui-focus);outline-offset:3px}@media(max-width:640px){.lesson-intro{padding:20px 16px 40px}.lesson-intro header{padding:22px}.lesson-intro h1{font-size:25px}.intro-rule-grid{grid-template-columns:minmax(0,1fr);gap:12px}.intro-rule-grid>section,.intro-next,.intro-teacher-note{padding:20px}.intro-next button{width:100%;justify-content:center}}