:root{
  --primary:#1967d2;
  --primary-dark:#104a9b;
  --primary-soft:#eaf2ff;
  --bg:#edf3fb;
  --surface:#ffffff;
  --surface-soft:#f8fbff;
  --line:#d5e0ef;
  --text:#142033;
  --muted:#617087;
  --ok:#087f5b;
  --ok-bg:#eefbf6;
  --warn:#9a6700;
  --warn-bg:#fff8dc;
  --danger:#b42318;
  --danger-bg:#fff2f1;
  --shadow:0 6px 18px rgba(15,23,42,.08);
  --radius:14px;
}
*{box-sizing:border-box}
html{scroll-behavior:smooth}
body{margin:0;min-height:100vh;font-family:"Segoe UI",Arial,sans-serif;background:var(--bg);color:var(--text);line-height:1.55}
button,input,select{font:inherit}
button{touch-action:manipulation}
a{color:var(--primary-dark)}
.site-header{height:50px;background:var(--primary);color:#fff;display:flex;align-items:center;justify-content:space-between;gap:16px;padding:0 18px;box-shadow:0 2px 8px #0002;position:relative;z-index:50}
.brand-link{display:flex;align-items:center;gap:9px;color:#fff;text-decoration:none;font-weight:800}
.brand-mark{display:grid;place-items:center;width:30px;height:30px;border:1px solid #ffffff80;border-radius:8px;background:#ffffff18;font-size:12px}
.site-header>strong{font-size:15px}

.series-home{max-width:1080px;margin:0 auto;padding:34px 18px 46px}
.intro-card{background:var(--surface);border:1px solid var(--line);border-radius:18px;padding:28px;box-shadow:var(--shadow);margin-bottom:22px}
.eyebrow{display:inline-block;background:var(--primary-soft);border:1px solid #bfd5f5;color:var(--primary-dark);border-radius:999px;padding:5px 10px;font-size:12px;font-weight:800;margin-bottom:10px}
.intro-card h1{font-size:34px;line-height:1.1;color:var(--primary-dark);margin:0 0 9px}
.intro-card p{max-width:780px;font-size:16px;margin:0}
.series-grid{display:grid;grid-template-columns:repeat(3,minmax(0,1fr));gap:16px}
.series-card{min-height:165px;border:1px solid var(--line);border-radius:16px;background:var(--surface);padding:22px;text-align:left;display:flex;flex-direction:column;justify-content:flex-end;gap:6px;box-shadow:var(--shadow)}
.series-card.active{cursor:pointer;background:linear-gradient(135deg,#fff,#edf5ff);border-color:#b9d3f6;transition:.18s ease}
.series-card.active:hover{transform:translateY(-2px);box-shadow:0 10px 24px rgba(25,103,210,.14)}
.series-card.disabled{opacity:.58}
.series-label{font-size:24px;font-weight:900;color:var(--primary-dark)}
.series-card strong{color:var(--primary);font-size:15px}

.course-view{min-height:calc(100vh - 50px)}
.course-toolbar{height:48px;background:var(--surface);border-bottom:1px solid var(--line);display:flex;align-items:center;gap:8px;padding:7px 14px;position:relative;z-index:45}
.pill-button,.series-pill{border-radius:999px;padding:7px 13px;font-size:12.5px;font-weight:800;white-space:nowrap}
.pill-button{border:1px solid #bdd2ef;background:#fff;color:var(--primary-dark);cursor:pointer}
.pill-button:hover{background:var(--primary-soft)}
.series-pill{background:var(--primary);color:#fff;border:1px solid var(--primary)}
.menu-toggle{display:none;margin-left:auto}
.course-layout{height:calc(100vh - 98px);display:grid;grid-template-columns:250px 1fr;min-width:0}
.lesson-menu{background:#fff;border-right:1px solid var(--line);overflow-y:auto;padding:10px 8px}
.menu-group-title{font-size:10px;text-transform:uppercase;letter-spacing:.08em;color:var(--muted);font-weight:900;padding:10px 8px 5px}
.menu-item{width:100%;display:block;border:0;background:transparent;text-align:left;color:#172033;font-size:12.5px;font-weight:700;line-height:1.25;padding:9px 9px;border-radius:8px;margin:2px 0;cursor:pointer}
.menu-item:hover{background:var(--primary-soft);color:var(--primary-dark)}
.menu-item.active{background:var(--primary);color:#fff;box-shadow:0 2px 7px rgba(25,103,210,.28)}
.content-area{padding:13px;overflow:hidden;min-width:0}
.lesson-heading{min-height:70px;display:flex;align-items:flex-start;justify-content:space-between;gap:18px;margin-bottom:9px}
.lesson-heading h2{font-size:24px;line-height:1.15;color:var(--primary-dark);margin:2px 0 0}
.unit-name{font-size:11px;font-weight:900;color:var(--primary);text-transform:uppercase;letter-spacing:.06em}
.technical-title{font-size:12px;font-weight:800;color:var(--muted);margin-top:2px}
.lesson-objective{font-size:13px;line-height:1.4;max-width:470px;text-align:right;margin:2px 0 0}
.lesson-content{height:calc(100vh - 98px - 26px - 70px - 9px);overflow-y:auto;background:var(--surface);border:1px solid var(--line);border-radius:13px;padding:24px;box-shadow:var(--shadow)}
.lesson-content h3{font-size:21px;color:var(--primary-dark);margin:24px 0 8px}
.lesson-content h3:first-child{margin-top:0}
.lesson-content h4{font-size:16.5px;color:var(--primary-dark);margin:0 0 7px}
.lesson-content p{margin:7px 0}
.lesson-content ul,.lesson-content ol{margin:8px 0 12px 22px;padding:0}
.lesson-content li{margin:5px 0}
.lesson-content strong{font-weight:800}

.hero-box,.concept-box,.example-box,.visual-box,.task-box,.exam-box,.note-box,.ok-box,.danger-box,.recall-box,.teacher-use{border-radius:12px;padding:15px 16px;margin:14px 0}
.hero-box{background:linear-gradient(135deg,var(--primary-soft),#fff);border:1px solid #bdd4f4}
.concept-box,.example-box,.visual-box,.recall-box{background:var(--surface-soft);border:1px solid var(--line)}
.task-box{background:#f8fbff;border:1px solid var(--line);border-left:5px solid var(--primary)}
.exam-box{background:#f5f2ff;border:1px solid #ded5ff;border-left:5px solid #6d4aff}
.note-box{background:var(--warn-bg);border-left:5px solid #d59b00}
.ok-box{background:var(--ok-bg);border-left:5px solid var(--ok)}
.danger-box{background:var(--danger-bg);border-left:5px solid var(--danger)}
.card-title{display:block;color:var(--primary-dark);font-weight:900;margin-bottom:5px}
.math{font-family:Cambria,"Times New Roman",serif;font-size:1.08em}
.formula{display:inline-block;background:#f2f6fb;border:1px solid var(--line);border-radius:8px;padding:5px 9px;font-family:Cambria,"Times New Roman",serif;font-size:1.1em;margin:3px 0}
.table-wrap{overflow-x:auto;margin:12px 0}
table{width:100%;border-collapse:collapse;background:#fff}
th,td{border:1px solid var(--line);padding:9px 10px;text-align:left;vertical-align:top}
th{background:var(--primary-soft);color:var(--primary-dark)}
.two-col,.three-col{display:grid;gap:12px;margin:14px 0}
.two-col{grid-template-columns:repeat(2,minmax(0,1fr))}
.three-col{grid-template-columns:repeat(3,minmax(0,1fr))}
.mini-card{background:#fff;border:1px solid var(--line);border-radius:10px;padding:13px}
.mini-card strong{display:block;color:var(--primary-dark);margin-bottom:4px}
.steps{counter-reset:step;list-style:none!important;margin-left:0!important}
.steps li{counter-increment:step;position:relative;padding-left:34px;min-height:28px;margin:8px 0}
.steps li::before{content:counter(step);position:absolute;left:0;top:0;width:24px;height:24px;display:grid;place-items:center;border-radius:50%;background:var(--primary);color:#fff;font-size:12px;font-weight:900}
.solution{margin-top:10px;border-top:1px dashed #cbd6e5;padding-top:8px}
.solution summary{cursor:pointer;color:var(--primary-dark);font-weight:800}
.solution[open] summary{margin-bottom:7px}
.quick-check{display:grid;gap:9px;margin:12px 0}
.quick-check label{display:flex;align-items:flex-start;gap:8px;background:#fff;border:1px solid var(--line);border-radius:9px;padding:9px 10px}
.quick-check input{margin-top:4px}

.quiz-item{border:1px solid var(--line);border-radius:10px;padding:13px;margin:10px 0;background:#fff}
.quiz-item>p{font-weight:800;margin:0 0 7px}
.quiz-item label{display:block;padding:5px 0;cursor:pointer}
.quiz-actions,.exercise-actions{display:flex;gap:8px;flex-wrap:wrap;margin-top:13px}
.action-button{border:1px solid #b9d3f6;background:#fff;color:var(--primary-dark);font-weight:800;border-radius:8px;padding:9px 12px;cursor:pointer}
.action-button.primary{background:var(--primary);color:#fff;border-color:var(--primary)}
.action-button.success{background:var(--ok);color:#fff;border-color:var(--ok)}
.action-button:hover{filter:brightness(.98)}
.quiz-result{margin-top:14px}
.review-grid{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:10px;margin-top:12px}
.review-card{background:#fff;border:1px solid var(--line);border-radius:10px;padding:12px}
.review-card strong{display:block;color:var(--primary-dark)}

.math-graph{width:100%;max-width:620px;height:auto;display:block;margin:10px auto}
.graph-axis{stroke:#607089;stroke-width:2}
.graph-grid{stroke:#dbe4ef;stroke-width:1}
.graph-line{stroke:#1967d2;stroke-width:4;fill:none}
.graph-alt{stroke:#e07a15;stroke-width:4;fill:none}
.graph-point{fill:#1967d2}
.graph-text{fill:#4b5b72;font-size:12px}
.number-line{display:flex;align-items:center;gap:6px;flex-wrap:wrap;margin:10px 0}
.number-chip{padding:6px 9px;border-radius:8px;background:var(--primary-soft);border:1px solid #bdd4f4;font-weight:800}

.exercise-panel{border:1px solid var(--line);border-radius:12px;padding:16px;background:#fff;margin-top:12px}
.exercise-controls{display:grid;grid-template-columns:2fr 1fr;gap:10px;margin-bottom:12px}
.exercise-controls label{font-size:12px;font-weight:800;color:var(--muted)}
.exercise-controls select{width:100%;margin-top:4px;border:1px solid var(--line);border-radius:8px;padding:9px;background:#fff;color:var(--text)}
.exercise-meta{display:flex;gap:8px;flex-wrap:wrap;margin-bottom:8px}
.badge{display:inline-block;border-radius:999px;background:var(--primary-soft);color:var(--primary-dark);padding:4px 8px;font-size:11px;font-weight:900}
.exercise-question{font-size:17px;font-weight:800;margin:9px 0 12px}
.exercise-feedback{margin-top:11px}
.exercise-progress{margin-top:12px;font-size:12px;color:var(--muted)}
.print-sheet{display:none}

@media(max-width:1100px){
  .course-layout{grid-template-columns:215px 1fr}
  .lesson-objective{max-width:380px}
}
@media(max-width:900px){
  .menu-toggle{display:inline-block}
  .course-layout{display:block;height:auto}
  .lesson-menu{display:none;position:fixed;inset:98px 0 0 0;z-index:40;border-right:0;padding:12px;overflow:auto}
  .lesson-menu.open{display:block}
  .content-area{overflow:visible;padding:10px}
  .lesson-heading{min-height:0;flex-direction:column;gap:3px;margin-bottom:10px}
  .lesson-objective{max-width:none;text-align:left}
  .lesson-content{height:auto;min-height:calc(100vh - 190px);overflow:visible}
}
@media(max-width:720px){
  .site-header{padding:0 10px}
  .site-header>strong{font-size:13px}
  .series-home{padding:18px 10px 30px}
  .intro-card{padding:20px}
  .intro-card h1{font-size:27px}
  .series-grid{grid-template-columns:1fr}
  .series-card{min-height:125px}
  .course-toolbar{padding:6px 8px}
  .content-area{padding:8px}
  .lesson-heading h2{font-size:20px}
  .lesson-content{padding:16px;border-radius:10px}
  .lesson-content h3{font-size:19px}
  .two-col,.three-col,.review-grid,.exercise-controls{grid-template-columns:1fr}
}
@media print{
  body{background:#fff;color:#000}
  .site-header,.course-toolbar,.lesson-menu,.lesson-heading,.exercise-controls,.exercise-actions,.exercise-progress{display:none!important}
  .course-layout,.content-area{display:block;height:auto;padding:0}
  .lesson-content{display:none!important}
  .print-sheet{display:block!important;padding:0 12mm;font-family:Arial,sans-serif}
  .print-sheet h1{font-size:20pt}
  .print-sheet h2{font-size:13pt;margin-top:16px}
  .print-item{break-inside:avoid;margin:13px 0 18px}
  .print-answer{display:none}
}