:root {
  --font-body: "Segoe UI", "Roboto", "Arial", sans-serif;
  --page-max-width: 1280px;
  --radius-lg: 24px;
  --radius-md: 18px;
  --radius-sm: 12px;
  --shadow-dark: 0 22px 48px rgba(0, 0, 0, 0.3);
  --shadow-light: 0 20px 40px rgba(100, 116, 139, 0.14);
}

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

html {
  font-size: 16px;
}

body {
  margin: 0;
  font-family: var(--font-body);
  line-height: 1.7;
  color: var(--text-color);
  background: var(--page-bg);
  transition: background-color 180ms ease, color 180ms ease;
}

body:not(.is-authorized) {
  overflow: hidden;
}

body.dark-theme {
  --page-bg: #07152f;
  --page-bg-alt: #0d2147;
  --panel-bg: #122c5d;
  --panel-bg-strong: #183873;
  --panel-border: rgba(173, 201, 255, 0.16);
  --menu-panel-bg: #0d2450;
  --menu-panel-strong: #143066;
  --menu-panel-border: rgba(120, 180, 255, 0.24);
  --lesson-panel-bg: #183465;
  --lesson-panel-strong: #21437e;
  --lesson-panel-border: rgba(255, 215, 0, 0.12);
  --panel-shadow: var(--shadow-dark);
  --text-color: #ffffff;
  --muted-text: #d7e4ff;
  --h1-color: #ffd700;
  --h2-color: #66ff66;
  --h3-color: #66ccff;
  --h4-color: #ff6666;
  --accent: #8cc7ff;
  --accent-strong: #dbeafe;
  --button-bg: rgba(255, 255, 255, 0.06);
  --button-hover: rgba(255, 255, 255, 0.14);
  --button-active: rgba(140, 199, 255, 0.18);
  --code-bg: rgba(255, 255, 255, 0.08);
  --quote-border: rgba(255, 215, 0, 0.38);
  --hero-highlight: rgba(255, 215, 0, 0.18);
}

body.light-theme {
  --page-bg: #f2f2f2;
  --page-bg-alt: #e3e6ea;
  --panel-bg: #ffffff;
  --panel-bg-strong: #f9fafb;
  --panel-border: rgba(15, 23, 42, 0.1);
  --menu-panel-bg: #f8fbff;
  --menu-panel-strong: #eef4fb;
  --menu-panel-border: rgba(29, 78, 216, 0.14);
  --lesson-panel-bg: #ffffff;
  --lesson-panel-strong: #fdfefe;
  --lesson-panel-border: rgba(15, 23, 42, 0.1);
  --panel-shadow: var(--shadow-light);
  --text-color: #000000;
  --muted-text: #4b5563;
  --h1-color: #b8860b;
  --h2-color: #006400;
  --h3-color: #0000cd;
  --h4-color: #8b0000;
  --accent: #1d4ed8;
  --accent-strong: #1e3a8a;
  --button-bg: #f3f4f6;
  --button-hover: #e5e7eb;
  --button-active: #dbe4f3;
  --code-bg: #eef2f7;
  --quote-border: rgba(184, 134, 11, 0.28);
  --hero-highlight: rgba(29, 78, 216, 0.1);
}

body.dark-theme {
  background:
    radial-gradient(circle at top left, rgba(255, 255, 255, 0.05), transparent 22rem),
    radial-gradient(circle at bottom right, rgba(102, 204, 255, 0.08), transparent 26rem),
    linear-gradient(180deg, var(--page-bg-alt), var(--page-bg));
}

body.light-theme {
  background:
    radial-gradient(circle at top left, rgba(255, 255, 255, 0.92), transparent 22rem),
    linear-gradient(180deg, var(--page-bg-alt), var(--page-bg));
}

a {
  color: var(--accent);
}

img {
  display: block;
  max-width: 100%;
  height: auto;
}

code,
pre {
  font-family: "Cascadia Mono", "Consolas", "Courier New", monospace;
}

.site-shell {
  width: min(100% - 2rem, var(--page-max-width));
  margin: 0 auto;
  padding: 1rem 0 2rem;
}

body:not(.is-authorized) .site-shell {
  visibility: hidden;
}

.auth-screen[hidden] {
  display: none;
}

.auth-screen {
  position: fixed;
  inset: 0;
  z-index: 80;
  display: grid;
  place-items: center;
  padding: 1rem;
  background:
    radial-gradient(circle at top, var(--hero-highlight), transparent 24rem),
    linear-gradient(180deg, var(--page-bg-alt), var(--page-bg));
}

.auth-card {
  width: min(100%, 42rem);
  padding: clamp(1.35rem, 3vw, 2rem);
  border: 1px solid var(--panel-border);
  border-radius: var(--radius-lg);
  background: linear-gradient(135deg, var(--panel-bg-strong), var(--panel-bg));
  box-shadow: var(--panel-shadow);
}

.auth-logo {
  width: min(100%, 28rem);
  height: auto;
  max-height: 14rem;
  object-fit: contain;
  display: block;
  margin: 0 auto 1rem;
}

body.is-authorized .auth-screen {
  display: none;
}

.auth-title {
  margin: 0.35rem 0 0.7rem;
  color: var(--h1-color);
  font-size: clamp(1.8rem, 3vw, 2.6rem);
  line-height: 1.1;
}

.auth-text,
.auth-message {
  margin: 0;
  color: var(--muted-text);
}

.auth-form {
  display: grid;
  gap: 0.8rem;
  margin-top: 1.1rem;
}

.auth-label {
  font-weight: 700;
}

.auth-input {
  width: 100%;
  padding: 0.9rem 1rem;
  border: 1px solid var(--panel-border);
  border-radius: var(--radius-md);
  background: var(--button-bg);
  color: var(--text-color);
  font: inherit;
}

.auth-input:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
}

.auth-submit,
.logout-button {
  padding: 0.85rem 1rem;
  border: 1px solid var(--panel-border);
  border-radius: 999px;
  background: var(--button-bg);
  color: var(--text-color);
  font: inherit;
  font-weight: 700;
  cursor: pointer;
}

.logout-button {
  min-width: 3.25rem;
  width: 3.25rem;
  height: 3.25rem;
  padding: 0;
  display: inline-flex;
  align-items: center;
  justify-content: center;
}

.logout-button__icon {
  width: 1.7rem;
  height: 1.7rem;
}

.auth-submit:hover,
.auth-submit:focus-visible,
.logout-button:hover,
.logout-button:focus-visible {
  background: var(--button-hover);
}

.auth-message {
  min-height: 1.5rem;
}

.site-header {
  display: grid;
  grid-template-columns: minmax(0, 1fr) auto;
  gap: 1rem;
  align-items: center;
  padding: 1.1rem 1.25rem;
  margin: 1rem 0 1.5rem;
  border: 1px solid var(--panel-border);
  border-radius: var(--radius-lg);
  background: linear-gradient(135deg, var(--panel-bg-strong), var(--panel-bg));
  box-shadow: var(--panel-shadow);
}

.site-header__copy {
  min-width: 0;
}

.site-brand {
  display: flex;
  align-items: center;
  gap: 0.85rem;
  margin: 0.2rem 0 0.35rem;
}

.site-brand__logo {
  width: 3.25rem;
  height: 3.25rem;
  object-fit: contain;
  flex-shrink: 0;
}

.site-header__actions {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  justify-self: end;
}

.eyebrow,
.site-subtitle,
.toc-panel__header p,
.lesson-meta,
.home-hero__lead {
  margin: 0;
  color: var(--muted-text);
}

.eyebrow {
  text-transform: uppercase;
  letter-spacing: 0.18em;
  font-size: 0.76rem;
}

.site-title {
  margin: 0;
  color: var(--h1-color);
  font-size: clamp(2rem, 3vw, 3rem);
  line-height: 1.08;
}

.site-subtitle {
  max-width: 42rem;
}

.menu-toggle,
.theme-toggle {
  border: 1px solid var(--panel-border);
  background: var(--button-bg);
  color: var(--text-color);
  cursor: pointer;
}

.menu-toggle {
  display: none;
  width: 3rem;
  height: 3rem;
  padding: 0.7rem;
  border-radius: 999px;
  align-items: center;
  justify-content: center;
  gap: 0.2rem;
  flex-direction: column;
}

.menu-toggle__line {
  width: 1.1rem;
  height: 2px;
  border-radius: 999px;
  background: currentColor;
}

.theme-toggle {
  min-width: 3.25rem;
  width: 3.25rem;
  height: 3.25rem;
  padding: 0;
  border-radius: 999px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  position: relative;
  font: inherit;
  font-weight: 700;
  transition: transform 160ms ease, background-color 160ms ease, border-color 160ms ease;
}

.theme-toggle__icon {
  position: absolute;
  width: 1.55rem;
  height: 1.55rem;
  transition: opacity 160ms ease, transform 160ms ease;
}

.theme-toggle__icon--sun {
  opacity: 0;
  transform: scale(0.7) rotate(-20deg);
}

.theme-toggle__icon--moon {
  opacity: 1;
  transform: scale(1) rotate(0deg);
}

body.light-theme .theme-toggle__icon--sun {
  opacity: 1;
  transform: scale(1) rotate(0deg);
}

body.light-theme .theme-toggle__icon--moon {
  opacity: 0;
  transform: scale(0.7) rotate(20deg);
}

.menu-toggle:hover,
.menu-toggle:focus-visible,
.theme-toggle:hover,
.theme-toggle:focus-visible,
.toc-button:hover,
.toc-button:focus-visible {
  background: var(--button-hover);
}

.theme-toggle:hover,
.theme-toggle:focus-visible {
  transform: translateY(-1px);
}

.mobile-backdrop {
  display: none;
}

.layout {
  display: grid;
  grid-template-columns: minmax(270px, 320px) minmax(0, 1fr);
  gap: 1.25rem;
  align-items: start;
}

.toc-panel,
.lesson-card,
.home-panel {
  border: 1px solid var(--panel-border);
  border-radius: var(--radius-lg);
  background: var(--panel-bg);
  box-shadow: var(--panel-shadow);
}

.toc-panel {
  position: sticky;
  top: 1rem;
  padding: 1rem;
  background: linear-gradient(180deg, var(--menu-panel-strong), var(--menu-panel-bg));
  border-color: var(--menu-panel-border);
}

.toc-panel__header {
  margin-bottom: 1rem;
}

.toc-panel__header h2 {
  margin: 0 0 0.25rem;
  color: var(--h2-color);
  font-size: 1.55rem;
}

.toc {
  display: grid;
  gap: 0.75rem;
}

.book-group {
  display: grid;
  gap: 0.6rem;
}

.book-toggle {
  width: 100%;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 0.75rem;
  padding: 0.95rem 1rem;
  border: 1px solid var(--menu-panel-border);
  border-radius: var(--radius-md);
  background: linear-gradient(180deg, var(--menu-panel-strong), var(--menu-panel-bg));
  color: var(--text-color);
  font: inherit;
  font-weight: 700;
  text-align: left;
  cursor: pointer;
  transition: background-color 160ms ease, border-color 160ms ease, transform 160ms ease;
}

.book-toggle:hover,
.book-toggle:focus-visible {
  background: var(--button-hover);
  transform: translateX(2px);
}

.book-toggle.is-open {
  border-color: var(--accent);
}

.book-toggle__title {
  font-size: 1rem;
}

.book-toggle__icon {
  width: 0.7rem;
  height: 0.7rem;
  border-right: 2px solid currentColor;
  border-bottom: 2px solid currentColor;
  transform: rotate(45deg);
  transition: transform 160ms ease;
}

.book-toggle.is-open .book-toggle__icon {
  transform: rotate(225deg);
}

.book-lessons {
  display: none;
  gap: 0.5rem;
  padding-left: 0.6rem;
}

.book-group.is-open .book-lessons {
  display: grid;
}

.toc-button {
  width: 100%;
  display: grid;
  gap: 0.15rem;
  padding: 0.95rem 1rem;
  border: 1px solid var(--menu-panel-border);
  border-radius: var(--radius-md);
  background: color-mix(in srgb, var(--menu-panel-bg) 82%, white 18%);
  color: var(--text-color);
  text-align: left;
  cursor: pointer;
  transition: background-color 160ms ease, border-color 160ms ease, transform 160ms ease;
}

.toc-button.is-active {
  background: var(--button-active);
  border-color: var(--accent);
  box-shadow: inset 0 0 0 1px rgba(255, 255, 255, 0.06);
}

.toc-button__eyebrow {
  font-size: 0.74rem;
  letter-spacing: 0.14em;
  text-transform: uppercase;
  color: var(--muted-text);
}

.toc-button__title {
  font-size: 1rem;
  font-weight: 700;
}

.lesson-link {
  width: 100%;
  padding: 0.8rem 0.95rem;
  border: 1px solid rgba(255, 255, 255, 0.08);
  border-radius: 14px;
  background: rgba(255, 255, 255, 0.05);
  color: var(--text-color);
  font: inherit;
  text-align: left;
  cursor: pointer;
  transition: background-color 160ms ease, border-color 160ms ease;
}

.lesson-link:hover,
.lesson-link:focus-visible {
  background: var(--button-hover);
  border-color: var(--accent);
}

.lesson-link.is-active {
  background: var(--button-active);
  border-color: var(--accent);
}

.lesson-link__label {
  display: block;
  font-size: 0.96rem;
}

.lesson-stage {
  min-width: 0;
}

.content-panel {
  display: none;
}

.content-panel.is-visible {
  display: block;
}

.home-panel,
.lesson-card {
  overflow: hidden;
  padding: clamp(1rem, 2vw, 2rem);
}

.home-panel {
  background: linear-gradient(180deg, var(--lesson-panel-strong), var(--lesson-panel-bg));
  border-color: var(--lesson-panel-border);
}

.lesson-card {
  background: linear-gradient(180deg, var(--lesson-panel-strong), var(--lesson-panel-bg));
  border-color: var(--lesson-panel-border);
}

.home-hero {
  padding: clamp(1.2rem, 3vw, 2.4rem);
  border-radius: calc(var(--radius-lg) - 4px);
  background:
    radial-gradient(circle at top right, var(--hero-highlight), transparent 20rem),
    linear-gradient(135deg, var(--panel-bg-strong), var(--panel-bg));
}

.home-hero h2 {
  margin: 0.35rem 0 0.75rem;
  color: var(--h1-color);
  font-size: clamp(2rem, 3.2vw, 3.2rem);
  line-height: 1.08;
}

.home-hero__lead {
  max-width: 52rem;
  font-size: 1.05rem;
}

.home-hero__actions {
  margin-top: 1.2rem;
}

.theme-toggle--hero {
  min-width: 3.25rem;
}

.home-grid {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 1rem;
  margin-top: 1rem;
}

.home-card {
  padding: 1.15rem;
  border: 1px solid var(--panel-border);
  border-radius: var(--radius-md);
  background: var(--button-bg);
}

.home-card h3 {
  margin: 0 0 0.5rem;
  color: var(--h3-color);
  font-size: 1.2rem;
}

.home-card p {
  margin: 0;
}

.lesson-meta {
  margin-bottom: 1rem;
  font-size: 0.82rem;
  font-weight: 700;
  letter-spacing: 0.14em;
}

.lesson-content > :first-child {
  margin-top: 0;
}

.lesson-content h1,
.lesson-content h2,
.lesson-content h3,
.lesson-content h4 {
  line-height: 1.2;
  margin: 1.5rem 0 0.7rem;
}

.lesson-content h1 {
  color: var(--h1-color);
  font-size: clamp(2rem, 3vw, 2.6rem);
}

.lesson-content h2 {
  color: var(--h2-color);
  font-size: clamp(1.55rem, 2.3vw, 2rem);
}

.lesson-content h3 {
  color: var(--h3-color);
  font-size: clamp(1.25rem, 1.9vw, 1.55rem);
}

.lesson-content h4 {
  color: var(--h4-color);
  font-size: clamp(1.05rem, 1.6vw, 1.2rem);
}

.lesson-content p,
.lesson-content ul,
.lesson-content ol,
.lesson-content blockquote,
.lesson-content pre,
.lesson-content table {
  margin: 0 0 1rem;
}

.lesson-content ul,
.lesson-content ol {
  padding-left: 1.5rem;
}

.lesson-content li + li {
  margin-top: 0.35rem;
}

.lesson-content blockquote {
  padding: 0.4rem 0 0.4rem 1rem;
  border-left: 4px solid var(--quote-border);
  color: var(--muted-text);
}

.lesson-content pre,
.lesson-content code {
  background: var(--code-bg);
  border-radius: 0.6rem;
}

.lesson-content code {
  padding: 0.15rem 0.4rem;
}

.lesson-content pre {
  padding: 1rem;
  overflow-x: auto;
}

.lesson-content table {
  width: 100%;
  border-collapse: collapse;
  display: block;
  overflow-x: auto;
}

.lesson-content th,
.lesson-content td {
  padding: 0.75rem;
  border: 1px solid var(--panel-border);
  text-align: left;
}

.lesson-content img {
  border-radius: var(--radius-sm);
  margin: 1.25rem auto;
}

@media (max-width: 980px) {
  .home-grid {
    grid-template-columns: 1fr;
  }
}

@media (max-width: 860px) {
  .site-shell {
    width: min(100% - 1rem, var(--page-max-width));
  }

  .site-header {
    grid-template-columns: minmax(0, 1fr) auto;
    align-items: start;
  }

  .menu-toggle {
    display: inline-flex;
  }

  .layout {
    grid-template-columns: 1fr;
  }

  .mobile-backdrop {
    position: fixed;
    inset: 0;
    z-index: 20;
    background: rgba(15, 23, 42, 0.42);
  }

  .toc-panel {
    position: fixed;
    top: 0;
    left: 0;
    bottom: 0;
    z-index: 30;
    width: min(84vw, 340px);
    border-radius: 0 24px 24px 0;
    transform: translateX(-105%);
    transition: transform 180ms ease;
    overflow-y: auto;
  }

  .toc-panel.is-open {
    transform: translateX(0);
  }

  .mobile-backdrop:not([hidden]) {
    display: block;
  }
}

@media (max-width: 560px) {
  html {
    font-size: 15px;
  }

  .site-shell {
    width: min(100% - 0.75rem, var(--page-max-width));
    padding-bottom: 1rem;
  }

  .site-header,
  .home-panel,
  .lesson-card {
    border-radius: 18px;
  }

  .site-header {
    padding: 1rem;
  }

  .site-brand {
    gap: 0.7rem;
  }

  .site-brand__logo {
    width: 2.8rem;
    height: 2.8rem;
  }

  .site-header__actions {
    flex-direction: column;
    align-items: stretch;
  }

  .theme-toggle {
    min-width: 3rem;
    width: 3rem;
    height: 3rem;
  }

  .logout-button {
    min-width: 3rem;
    width: 3rem;
    height: 3rem;
  }

  .home-hero {
    padding: 1.1rem;
  }

  .toc-button {
    padding: 0.85rem 0.9rem;
  }
}