/* ==========================================================================
   Теорема Виета — Стили (vieta.css)
   Поддерживает единую дизайн-систему с Алканами: шрифты Syne, Manrope, IBM Plex Sans
   ========================================================================== */

:root {
  --ink: #0c1f22;
  --muted: #3f5c61;
  --paper: #f2f7f6;
  --paper-2: #e4efed;
  --teal: #08756f;
  --teal-deep: #033d3a;
  --mint: #b8e0db;
  --lime: #c6e36a;
  --amber: #d97706;
  --amber-deep: #92400e;
  --amber-light: #fef3c7;
  --wrong: #b54a3c;
  --wrong-bg: #fdf0ee;
  --right: #1f7a4d;
  --right-bg: #eaf6ef;
  --radius: 8px;
  --radius-lg: 14px;
  --font-display: "Syne", sans-serif;
  --font-body: "Manrope", sans-serif;
  --font-math: "IBM Plex Sans", -apple-system, sans-serif;
  --shadow-soft: 0 16px 45px rgba(12, 31, 34, 0.07);
}

*,
*::before,
*::after {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  min-height: 100vh;
  font-family: var(--font-body);
  color: var(--ink);
  background: var(--paper);
  line-height: 1.55;
  overflow-x: hidden;
  -webkit-tap-highlight-color: transparent;
}

/* Фоны и атмосфера */
.atmosphere {
  position: fixed;
  inset: 0;
  z-index: -1;
  background:
    radial-gradient(ellipse 90% 60% at 5% -10%, rgba(254, 243, 199, 0.7), transparent 55%),
    radial-gradient(ellipse 70% 50% at 95% 15%, rgba(184, 224, 219, 0.8), transparent 50%),
    radial-gradient(ellipse 60% 40% at 50% 100%, rgba(8, 117, 111, 0.1), transparent 55%),
    linear-gradient(165deg, #f7faf8 0%, #f4f8f6 45%, #eaf3f0 100%);
  pointer-events: none;
}

.atmosphere::after {
  content: "";
  position: absolute;
  inset: 0;
  opacity: 0.3;
  background-image: url("data:image/svg+xml,%3Csvg width='60' height='60' viewBox='0 0 60 60' xmlns='http://www.w3.org/2000/svg'%3E%3Cg fill='none' stroke='%230b7a74' stroke-opacity='0.08' stroke-width='1'%3E%3Ccircle cx='8' cy='8' r='1.5'/%3E%3Ccircle cx='30' cy='30' r='1.5'/%3E%3Ccircle cx='52' cy='8' r='1.5'/%3E%3Cpath d='M8 8h44M8 8v44'/%3E%3C/g%3E%3C/svg%3E");
}

a {
  color: inherit;
  text-decoration: none;
}

/* Навигация */
.top-nav {
  position: sticky;
  top: 0;
  z-index: 100;
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  background: rgba(242, 247, 246, 0.88);
  border-bottom: 1px solid rgba(11, 122, 116, 0.12);
  padding: 0.75rem clamp(1.25rem, 4vw, 3rem);
}

.top-nav-inner {
  max-width: 1200px;
  margin: 0 auto;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  font-size: 0.92rem;
}

.nav-back-link {
  display: inline-flex;
  align-items: center;
  gap: 0.45rem;
  font-weight: 700;
  color: var(--teal-deep);
  transition: color 0.18s ease, transform 0.18s ease;
}

.nav-back-link:hover {
  color: var(--teal);
  transform: translateX(-2px);
}

.nav-current {
  color: var(--muted);
  font-weight: 600;
  display: none;
}

@media (min-width: 640px) {
  .nav-current {
    display: inline;
  }
}

.nav-next-link {
  font-weight: 700;
  color: var(--teal);
  transition: color 0.18s ease;
}

.nav-next-link:hover {
  color: var(--teal-deep);
  text-decoration: underline;
}

/* Кнопки общего стиля */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.5rem;
  min-height: 2.85rem;
  padding: 0 1.25rem;
  border: 1.5px solid transparent;
  border-radius: var(--radius);
  font-family: var(--font-body);
  font-weight: 700;
  font-size: 0.95rem;
  cursor: pointer;
  transition: transform 0.18s ease, background 0.18s ease, border-color 0.18s ease, color 0.18s ease, box-shadow 0.18s ease;
}

.btn:hover:not(:disabled) {
  transform: translateY(-1px);
}

.btn:active:not(:disabled) {
  transform: translateY(0);
}

.btn:disabled,
.btn[disabled] {
  opacity: 0.45;
  cursor: not-allowed;
  filter: grayscale(35%);
  pointer-events: none;
  transform: none !important;
  box-shadow: none !important;
}

.btn-primary {
  background: var(--teal);
  color: #f7fffe;
}

.btn-primary:hover {
  background: var(--teal-deep);
}

.btn-ghost {
  background: transparent;
  border-color: rgba(16, 36, 40, 0.18);
  color: var(--ink);
}

.btn-ghost:hover {
  border-color: var(--teal);
  color: var(--teal-deep);
  background: rgba(8, 117, 111, 0.04);
}

.btn-accent {
  background: #0f766e;
  color: #fff;
}

.btn-accent:hover {
  background: #115e59;
}

/* Hero секция */
.hero {
  min-height: auto;
  padding: clamp(2.5rem, 6vh, 4.5rem) clamp(1.25rem, 4vw, 3rem) 2rem;
  max-width: 1200px;
  margin: 0 auto;
  display: grid;
  grid-template-columns: 1.2fr 0.8fr;
  gap: clamp(1.5rem, 4vw, 3.5rem);
  align-items: center;
}

.hero-copy {
  display: flex;
  flex-direction: column;
}

.badge-topic {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  align-self: flex-start;
  padding: 0.35rem 0.85rem;
  border-radius: 999px;
  background: var(--amber-light);
  color: var(--amber-deep);
  border: 1px solid rgba(217, 119, 6, 0.25);
  font-size: 0.82rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.03em;
  margin-bottom: 0.85rem;
}

.hero-title {
  margin: 0 0 1rem;
  font-family: var(--font-display);
  font-weight: 800;
  font-size: clamp(2.4rem, 5.2vw, 3.8rem);
  line-height: 1.05;
  letter-spacing: -0.04em;
  color: var(--teal-deep);
}

.hero-lede {
  margin: 0 0 1.75rem;
  color: var(--muted);
  font-size: 1.1rem;
  line-height: 1.6;
  max-width: 48ch;
}

.cta-row {
  display: flex;
  flex-wrap: wrap;
  gap: 0.85rem;
}

/* Hero карточка формулы */
.hero-card {
  background: rgba(255, 255, 255, 0.88);
  border: 1.5px solid rgba(8, 117, 111, 0.16);
  border-radius: var(--radius-lg);
  padding: 1.8rem;
  box-shadow: var(--shadow-soft);
  position: relative;
  overflow: hidden;
}

.hero-card::after {
  content: "";
  position: absolute;
  right: -20px;
  bottom: -20px;
  width: 140px;
  height: 140px;
  background: radial-gradient(circle, rgba(184, 224, 219, 0.45), transparent 70%);
  border-radius: 50%;
  pointer-events: none;
}

.card-equation-tag {
  font-size: 0.8rem;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  font-weight: 700;
  color: var(--muted);
  margin-bottom: 0.6rem;
}

.formula-main {
  font-family: var(--font-math);
  font-size: clamp(1.4rem, 2.5vw, 1.85rem);
  font-weight: 700;
  color: var(--teal-deep);
  margin-bottom: 1.25rem;
  padding-bottom: 1rem;
  border-bottom: 1px dashed rgba(8, 117, 111, 0.18);
}

.system-display {
  display: flex;
  align-items: stretch;
  gap: 0.85rem;
  font-family: var(--font-math);
  font-size: 1.15rem;
}

.bracket-svg {
  width: 15px;
  min-width: 15px;
  align-self: stretch;
  color: var(--teal);
  flex-shrink: 0;
  display: block;
}

.system-lines {
  display: flex;
  flex-direction: column;
  justify-content: center;
  gap: 0.65rem;
}

.system-line {
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.equation-lhs {
  display: inline-block;
  min-width: 5.6rem;
  font-weight: 600;
}

.math-accent {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-width: 2.2rem;
  background: #f1f8f6;
  padding: 0.15rem 0.55rem;
  border-radius: 6px;
  border: 1px solid rgba(8, 117, 111, 0.22);
  font-weight: 700;
  color: var(--teal);
  text-align: center;
}

/* Секции страницы */
.section {
  max-width: 1200px;
  margin: 0 auto;
  padding: clamp(2.5rem, 6vh, 4.5rem) clamp(1.25rem, 4vw, 3rem);
}

.section-head {
  max-width: 44rem;
  margin-bottom: 2.2rem;
}

.section-head h2 {
  margin: 0 0 0.5rem;
  font-family: var(--font-display);
  font-size: clamp(1.8rem, 3.4vw, 2.4rem);
  letter-spacing: -0.03em;
  color: var(--teal-deep);
}

.section-head p {
  margin: 0;
  color: var(--muted);
  font-size: 1.05rem;
}

/* Теория: Сетка карточек */
.theory-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(320px, 1fr));
  gap: 1.5rem;
  margin-bottom: 2.5rem;
}

.theory-card {
  background: rgba(255, 255, 255, 0.85);
  border: 1.5px solid rgba(8, 117, 111, 0.14);
  border-radius: var(--radius-lg);
  padding: 1.8rem;
  box-shadow: 0 8px 30px rgba(12, 31, 34, 0.04);
  display: flex;
  flex-direction: column;
}

.theory-card-header {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  margin-bottom: 1rem;
}

.theory-num {
  width: 32px;
  height: 32px;
  border-radius: 8px;
  background: var(--paper-2);
  color: var(--teal);
  font-family: var(--font-display);
  font-weight: 800;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 0.95rem;
  flex-shrink: 0;
}

.theory-card h3 {
  margin: 0;
  font-family: var(--font-display);
  font-size: 1.25rem;
  color: var(--ink);
}

.theory-card p {
  margin: 0 0 1rem;
  color: var(--muted);
  font-size: 0.95rem;
  line-height: 1.6;
}

.theory-box {
  background: var(--paper-2);
  border-left: 3px solid var(--teal);
  padding: 0.9rem 1.1rem;
  border-radius: 0 var(--radius) var(--radius) 0;
  font-family: var(--font-math);
  font-size: 0.96rem;
  margin-top: auto;
}

.theory-box code {
  font-weight: 700;
  color: var(--teal-deep);
}

/* Золотое правило знаков */
.signs-table-wrap {
  background: #fff;
  border: 1px solid rgba(8, 117, 111, 0.14);
  border-radius: var(--radius);
  overflow: hidden;
  margin-top: 0.5rem;
}

.signs-row {
  display: grid;
  grid-template-columns: 110px 1fr;
  padding: 0.65rem 0.85rem;
  border-bottom: 1px solid rgba(8, 117, 111, 0.08);
  font-size: 0.9rem;
  align-items: center;
}

.signs-row:last-child {
  border-bottom: none;
}

.signs-label {
  font-weight: 700;
  color: var(--teal-deep);
  font-family: var(--font-math);
}

.signs-desc {
  color: var(--muted);
}

/* Интерактивный калькулятор теоремы */
.calc-widget {
  background: rgba(255, 255, 255, 0.9);
  border: 1.5px solid rgba(8, 117, 111, 0.18);
  border-radius: var(--radius-lg);
  padding: clamp(1.5rem, 3vw, 2.2rem);
  box-shadow: var(--shadow-soft);
}

.calc-widget-head {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  margin-bottom: 1.5rem;
}

.calc-widget-head h3 {
  margin: 0;
  font-family: var(--font-display);
  font-size: 1.35rem;
  color: var(--teal-deep);
}

.calc-controls {
  display: flex;
  flex-wrap: wrap;
  gap: 1.25rem;
  align-items: flex-end;
  margin-bottom: 1.5rem;
  padding-bottom: 1.5rem;
  border-bottom: 1px dashed rgba(8, 117, 111, 0.16);
}

.input-group {
  display: flex;
  flex-direction: column;
  gap: 0.35rem;
}

.input-group label {
  font-size: 0.85rem;
  font-weight: 700;
  color: var(--muted);
  text-transform: uppercase;
  letter-spacing: 0.03em;
}

.calc-input {
  width: 90px;
  height: 2.85rem;
  padding: 0 0.75rem;
  border: 1.5px solid rgba(8, 117, 111, 0.25);
  border-radius: var(--radius);
  font-family: var(--font-math);
  font-size: 1.15rem;
  font-weight: 600;
  text-align: center;
  background: #fff;
  color: var(--ink);
  transition: border-color 0.18s ease, box-shadow 0.18s ease;
}

.calc-input:focus {
  outline: none;
  border-color: var(--teal);
  box-shadow: 0 0 0 3px rgba(8, 117, 111, 0.16);
}

.calc-result-box {
  background: var(--paper-2);
  border-radius: var(--radius);
  padding: 1.25rem;
}

.calc-step-line {
  margin-bottom: 0.75rem;
  font-family: var(--font-math);
  font-size: 1rem;
}

.calc-step-line:last-child {
  margin-bottom: 0;
}

/* ==========================================================================
   Тренажёр практики (Trainer Section)
   ========================================================================== */

.practice-section {
  padding-top: 1.5rem;
}

.practice-section .section-head,
.section.practice-section .section-head {
  max-width: 820px;
  margin: 0 auto 2rem;
}

.mode-switch {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
  max-width: 820px;
  margin: 0 auto 1.75rem;
}

.mode-btn {
  padding: 0.65rem 1.15rem;
  background: rgba(255, 255, 255, 0.75);
  border: 1.5px solid rgba(8, 117, 111, 0.15);
  border-radius: var(--radius);
  font-family: var(--font-body);
  font-weight: 700;
  font-size: 0.92rem;
  color: var(--muted);
  cursor: pointer;
  transition: all 0.18s ease;
}

.mode-btn:hover {
  background: #fff;
  border-color: var(--teal);
  color: var(--teal-deep);
}

.mode-btn.is-active {
  background: var(--teal);
  color: #fff;
  border-color: var(--teal);
  box-shadow: 0 4px 12px rgba(8, 117, 111, 0.25);
}

.trainer-card {
  background: rgba(255, 255, 255, 0.92);
  border: 1.5px solid rgba(8, 117, 111, 0.18);
  border-radius: var(--radius-lg);
  padding: clamp(1.5rem, 3.5vw, 2.5rem);
  box-shadow: var(--shadow-soft);
  max-width: 820px;
  margin: 0 auto;
}

.trainer-score-bar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 0.75rem 1.5rem;
  padding-bottom: 1.25rem;
  margin-bottom: 1.75rem;
  border-bottom: 1px solid rgba(8, 117, 111, 0.12);
  font-size: 0.92rem;
  color: var(--muted);
}

.score-badge {
  display: inline-flex;
  align-items: center;
  gap: 0.35rem;
}

.score-badge strong {
  color: var(--teal-deep);
  font-size: 1.1rem;
}

.streak-badge strong {
  color: #d97706;
}

.equation-display-wrap {
  text-align: center;
  padding: clamp(1.2rem, 3vw, 2rem) 1rem;
  background: linear-gradient(145deg, #f7faf9, #eef5f3);
  border-radius: var(--radius);
  border: 1px solid rgba(8, 117, 111, 0.12);
  margin-bottom: 1.75rem;
}

.equation-label {
  margin: 0 0 0.5rem;
  font-size: 0.85rem;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  font-weight: 700;
  color: var(--muted);
}

.equation-text {
  margin: 0;
  font-family: var(--font-math);
  font-size: clamp(2rem, 4.5vw, 3rem);
  font-weight: 700;
  color: var(--teal-deep);
  letter-spacing: -0.02em;
}

/* Блок подсказки */
.hint-toggle-wrap {
  display: flex;
  justify-content: center;
  margin-bottom: 1.25rem;
}

.btn-hint {
  font-size: 0.85rem;
  color: var(--muted);
  background: transparent;
  border: none;
  cursor: pointer;
  text-decoration: underline;
  padding: 0.3rem 0.6rem;
  transition: color 0.18s ease;
}

.btn-hint:hover {
  color: var(--teal);
}

.hint-box {
  background: var(--amber-light);
  border: 1px solid rgba(217, 119, 6, 0.25);
  border-radius: var(--radius);
  padding: 0.85rem 1.2rem;
  margin-bottom: 1.5rem;
  font-family: var(--font-math);
  font-size: 0.95rem;
  color: var(--amber-deep);
  animation: fade-in 0.25s ease;
}

/* Форма ответа */
.answer-form {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 1.5rem;
  margin-bottom: 1.5rem;
}

.inputs-row {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 1rem;
  flex-wrap: wrap;
}

.root-input-wrap {
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.root-label {
  font-family: var(--font-math);
  font-size: 1.35rem;
  font-weight: 700;
  color: var(--teal-deep);
}

.root-input {
  width: 90px;
  height: 3.2rem;
  border: 2px solid rgba(8, 117, 111, 0.25);
  border-radius: var(--radius);
  font-family: var(--font-math);
  font-size: 1.45rem;
  font-weight: 700;
  text-align: center;
  background: #fff;
  color: var(--ink);
  transition: all 0.18s ease;
}

.root-input:focus {
  outline: none;
  border-color: var(--teal);
  box-shadow: 0 0 0 4px rgba(8, 117, 111, 0.18);
}

.root-input.is-correct {
  border-color: var(--right);
  background: var(--right-bg);
  color: var(--right);
}

.root-input.is-wrong {
  border-color: var(--wrong);
  background: var(--wrong-bg);
  color: var(--wrong);
}

/* Кнопки проверки */
.trainer-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 0.75rem;
  justify-content: center;
  width: 100%;
}

.btn-check {
  min-width: 150px;
}

.btn-next {
  min-width: 180px;
  transition: all 0.22s ease;
}

.btn-next:not(:disabled) {
  background: var(--teal);
  color: #fff;
  box-shadow: 0 4px 14px rgba(8, 117, 111, 0.35);
  animation: pulse-ready 1.6s ease-in-out infinite;
}

@keyframes pulse-ready {
  0%, 100% {
    box-shadow: 0 4px 14px rgba(8, 117, 111, 0.35);
  }
  50% {
    box-shadow: 0 4px 22px rgba(8, 117, 111, 0.65);
    transform: translateY(-1px);
  }
}

/* Карточки обратной связи */
.feedback-box {
  border-radius: var(--radius);
  padding: 1.15rem 1.4rem;
  margin-bottom: 1.25rem;
  font-size: 1rem;
  line-height: 1.5;
  animation: rise 0.28s ease both;
}

.feedback-success {
  background: var(--right-bg);
  border: 1px solid rgba(31, 122, 77, 0.28);
  color: #0e4c2e;
}

.feedback-error {
  background: var(--wrong-bg);
  border: 1px solid rgba(181, 74, 60, 0.28);
  color: #782216;
}

.feedback-title {
  font-weight: 700;
  margin-bottom: 0.35rem;
  display: flex;
  align-items: center;
  gap: 0.4rem;
}

/* Пошаговое решение */
.solution-panel {
  background: #f8faf9;
  border: 1px solid rgba(8, 117, 111, 0.14);
  border-radius: var(--radius);
  padding: 1.25rem;
  margin-top: 1rem;
  font-size: 0.95rem;
  line-height: 1.6;
  animation: fade-in 0.25s ease;
}

.solution-panel h4 {
  margin: 0 0 0.75rem;
  font-family: var(--font-display);
  color: var(--teal-deep);
  font-size: 1.05rem;
}

.solution-panel ol {
  margin: 0;
  padding-left: 1.25rem;
}

.solution-panel li {
  margin-bottom: 0.5rem;
}

.solution-panel li:last-child {
  margin-bottom: 0;
}

/* Анимации */
@keyframes rise {
  from {
    opacity: 0;
    transform: translateY(8px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

@keyframes fade-in {
  from {
    opacity: 0;
  }
  to {
    opacity: 1;
  }
}

/* Футер */
.site-footer {
  margin-top: clamp(3rem, 7vh, 5.5rem);
  display: flex;
  flex-direction: column;
  align-items: center;
  text-align: center;
  gap: 0.45rem;
  padding: 2.5rem clamp(1.25rem, 4vw, 3rem) 3rem;
  border-top: 1px solid rgba(16, 36, 40, 0.08);
  background: linear-gradient(180deg, transparent, rgba(11, 122, 116, 0.06));
}

.footer-nav {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 0.65rem;
  margin-bottom: 0.35rem;
  font-size: 0.92rem;
  font-weight: 600;
}

.footer-nav a {
  color: var(--teal-deep);
  transition: color 0.18s ease;
}

.footer-nav a:hover {
  color: var(--teal);
  text-decoration: underline;
}

.footer-nav span {
  color: rgba(16, 36, 40, 0.28);
}

.footer-note {
  margin: 0;
  color: var(--muted);
  font-size: 0.92rem;
}

.visit-stats {
  margin: 0.15rem 0 0.35rem;
  color: var(--muted);
  font-size: 0.88rem;
  letter-spacing: 0.01em;
}

.visit-stats strong {
  color: var(--teal-deep);
  font-weight: 700;
  font-variant-numeric: tabular-nums;
}

.made-by {
  margin: 0;
  font-family: "IBM Plex Sans", var(--font-body), sans-serif;
  font-weight: 600;
  font-size: clamp(0.92rem, 1.6vw, 1.05rem);
  letter-spacing: 0.01em;
  color: var(--ink);
  line-height: 1.35;
}

.made-name {
  color: var(--teal-deep);
}

.made-handle {
  color: var(--teal);
  text-decoration: none;
  border-bottom: 2px solid rgba(8, 117, 111, 0.35);
  transition: border-color 0.2s ease, color 0.2s ease;
}

.made-handle:hover {
  color: var(--teal-deep);
  border-bottom-color: var(--teal-deep);
}

@media (max-width: 768px) {
  .hero {
    grid-template-columns: 1fr;
    padding-top: 2rem;
  }

  .calc-controls {
    align-items: stretch;
  }

  .calc-input {
    width: 100%;
  }

  .inputs-row {
    flex-direction: column;
    gap: 0.75rem;
  }

  .root-input-wrap {
    width: 100%;
    justify-content: center;
  }

  .root-input {
    width: 120px;
  }
}