*,
*::before,
*::after {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

:root {
  --bg: #0d0d0d;
  --bg-light: #1a1a1a;
  --bg-lighter: #242424;
  --text: #e8e8e8;
  --text-muted: #888;
  --accent: #c8956c;
  --accent-dim: rgba(200, 149, 108, 0.12);
  --border: rgba(255, 255, 255, 0.08);
  --sidebar-width: 220px;
  --input-bar-height: 80px;
}

html {
  font-size: 16px;
  scroll-behavior: smooth;
}

body {
  font-family: 'Space Grotesk', sans-serif;
  font-weight: 400;
  background: var(--bg);
  color: var(--text);
  line-height: 1.6;
  min-height: 100vh;
}

a {
  color: var(--accent);
  text-decoration: none;
}

a:hover {
  text-decoration: underline;
}

button {
  font-family: inherit;
  cursor: pointer;
  border: none;
  background: none;
  color: var(--text);
}

/* ──────────────────────────────
   Landing Page — Hero
   ────────────────────────────── */

.hero {
  position: relative;
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  background: url('../images/portrait.jpg') center / cover no-repeat;
  overflow: hidden;
}

.hero::before {
  content: '';
  position: absolute;
  inset: 0;
  background: linear-gradient(
    to bottom,
    rgba(10, 10, 10, 0.5) 0%,
    rgba(10, 10, 10, 0.85) 100%
  );
}

.hero-content {
  position: relative;
  text-align: center;
  padding: 2rem;
}

.hero-title {
  font-size: 3.5rem;
  font-weight: 700;
  line-height: 1.2;
  letter-spacing: -0.02em;
  margin-bottom: 1rem;
}

.hero-tagline {
  font-size: 1.25rem;
  color: var(--text-muted);
  max-width: 480px;
  margin: 0 auto;
}

/* ──────────────────────────────
   Landing Page — Concept List
   ────────────────────────────── */

.concept-list-section {
  padding: 4rem 2rem 6rem;
  max-width: 720px;
  margin: 0 auto;
}

.concept-list-container {
  display: flex;
  flex-direction: column;
  gap: 1px;
}

.concept-card {
  display: flex;
  align-items: flex-start;
  gap: 1.25rem;
  padding: 1.5rem;
  border-bottom: 1px solid var(--border);
  color: var(--text);
  transition: background 0.15s;
}

.concept-card:hover {
  background: var(--bg-light);
  text-decoration: none;
}

.concept-number {
  font-size: 0.85rem;
  font-weight: 700;
  color: var(--accent);
  min-width: 1.5rem;
  padding-top: 0.15rem;
}

.concept-card-body {
  flex: 1;
}

.concept-card-title {
  font-size: 1.25rem;
  font-weight: 700;
  line-height: 1.3;
  margin-bottom: 0.35rem;
}

.concept-card-description {
  font-size: 0.95rem;
  color: var(--text-muted);
  margin-bottom: 0.35rem;
}

.concept-card-domain {
  font-size: 0.8rem;
  color: var(--text-muted);
  opacity: 0.7;
}

/* ──────────────────────────────
   Concept Page — Layout
   ────────────────────────────── */

.sidebar {
  position: fixed;
  top: 0;
  left: 0;
  width: var(--sidebar-width);
  height: 100vh;
  background: var(--bg);
  border-right: 1px solid var(--border);
  display: flex;
  flex-direction: column;
  z-index: 100;
}

.sidebar-header {
  padding: 1.5rem 1.25rem;
  border-bottom: 1px solid var(--border);
}

.sidebar-title {
  font-size: 0.95rem;
  font-weight: 700;
  color: var(--text);
  letter-spacing: -0.01em;
}

.sidebar-title:hover {
  text-decoration: none;
  color: var(--accent);
}

.sidebar-nav {
  flex: 1;
  overflow-y: auto;
  padding: 0.75rem 0;
}

.sidebar .concept-list,
.mobile-menu .concept-list {
  list-style: none;
}

.sidebar .concept-list li a,
.mobile-menu .concept-list li a {
  display: block;
  padding: 0.6rem 1.25rem;
  font-size: 0.9rem;
  color: var(--text-muted);
  transition: color 0.15s, background 0.15s;
}

.sidebar .concept-list li a:hover,
.mobile-menu .concept-list li a:hover {
  color: var(--text);
  background: var(--bg-light);
  text-decoration: none;
}

.sidebar .concept-list li.active a,
.mobile-menu .concept-list li.active a {
  color: var(--accent);
  background: var(--accent-dim);
}

.main-content {
  margin-left: var(--sidebar-width);
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  position: relative;
}

/* ──────────────────────────────
   Mobile Header & Menu
   ────────────────────────────── */

.mobile-header {
  display: none;
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  height: 50px;
  background: var(--bg);
  border-bottom: 1px solid var(--border);
  align-items: center;
  padding: 0 1rem;
  z-index: 90;
}

.hamburger {
  display: flex;
  flex-direction: column;
  gap: 4px;
  padding: 0.5rem;
  background: none;
  border: none;
}

.hamburger span {
  display: block;
  width: 20px;
  height: 2px;
  background: var(--text);
  border-radius: 1px;
}

.mobile-title {
  font-size: 0.9rem;
  font-weight: 700;
  margin-left: 0.75rem;
}

.mobile-menu-backdrop {
  display: none;
  position: fixed;
  inset: 0;
  background: rgba(0, 0, 0, 0.6);
  z-index: 200;
}

.mobile-menu-backdrop.open {
  display: block;
}

.mobile-menu {
  position: fixed;
  top: 0;
  left: 0;
  width: 260px;
  height: 100vh;
  background: var(--bg);
  border-right: 1px solid var(--border);
  transform: translateX(-100%);
  transition: transform 0.25s ease;
  z-index: 210;
  padding-top: 1rem;
  overflow-y: auto;
}

.mobile-menu.open {
  transform: translateX(0);
}

.mobile-menu-close {
  position: absolute;
  top: 0.75rem;
  right: 0.75rem;
  font-size: 1.5rem;
  color: var(--text-muted);
  background: none;
  border: none;
  padding: 0.25rem 0.5rem;
}

/* ──────────────────────────────
   Conversation View
   ────────────────────────────── */

.conversation-view {
  flex: 1;
  display: flex;
  flex-direction: column;
  padding-bottom: var(--input-bar-height);
}

.chat-area {
  flex: 1;
  overflow-y: auto;
  padding: 2rem 1.5rem;
  max-width: 720px;
  width: 100%;
  margin: 0 auto;
}

.agent-label {
  font-size: 0.75rem;
  font-weight: 700;
  color: var(--accent);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-bottom: 0.5rem;
}

.chat-message {
  margin-bottom: 1.25rem;
  padding: 0.85rem 1.1rem;
  border-radius: 8px;
  max-width: 85%;
  line-height: 1.6;
  animation: messageIn 0.2s ease;
}

@keyframes messageIn {
  from {
    opacity: 0;
    transform: translateY(6px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

.chat-message.agent {
  background: var(--accent-dim);
  margin-right: auto;
  border-bottom-left-radius: 2px;
}

.chat-message.reader {
  background: var(--bg-lighter);
  margin-left: auto;
  border-bottom-right-radius: 2px;
}

.chat-message p {
  margin-bottom: 0.6rem;
}

.chat-message p:last-child {
  margin-bottom: 0;
}

.chat-message strong {
  font-weight: 700;
}

.chat-message em {
  font-style: italic;
}

.streaming-cursor::after {
  content: '\25AE';
  animation: blink 0.8s step-end infinite;
  color: var(--accent);
  margin-left: 2px;
}

@keyframes blink {
  50% {
    opacity: 0;
  }
}

.loading-indicator {
  display: flex;
  gap: 4px;
  padding: 0.85rem 1.1rem;
  margin-right: auto;
}

.loading-indicator span {
  width: 6px;
  height: 6px;
  border-radius: 50%;
  background: var(--text-muted);
  animation: loadingDot 1.2s ease-in-out infinite;
}

.loading-indicator span:nth-child(2) {
  animation-delay: 0.15s;
}

.loading-indicator span:nth-child(3) {
  animation-delay: 0.3s;
}

@keyframes loadingDot {
  0%, 60%, 100% {
    opacity: 0.3;
    transform: scale(0.8);
  }
  30% {
    opacity: 1;
    transform: scale(1);
  }
}

.error-message {
  color: var(--text-muted);
  font-style: italic;
}

/* ──────────────────────────────
   Input Bar
   ────────────────────────────── */

.input-bar {
  position: fixed;
  bottom: 0;
  right: 0;
  left: var(--sidebar-width);
  background: var(--bg);
  border-top: 1px solid var(--border);
  padding: 0.75rem 1.5rem;
  z-index: 50;
}

.input-bar-inner {
  display: flex;
  align-items: flex-end;
  gap: 0.5rem;
  max-width: 720px;
  margin: 0 auto;
}

#message-input {
  flex: 1;
  background: var(--bg-light);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 0.6rem 0.85rem;
  color: var(--text);
  font-family: inherit;
  font-size: 0.95rem;
  line-height: 1.5;
  resize: none;
  max-height: 6rem;
  overflow-y: auto;
}

#message-input::placeholder {
  color: var(--text-muted);
}

#message-input:focus {
  outline: none;
  border-color: rgba(255, 255, 255, 0.15);
}

.send-btn,
.article-toggle-btn {
  width: 38px;
  height: 38px;
  display: flex;
  align-items: center;
  justify-content: center;
  border-radius: 8px;
  color: var(--text-muted);
  transition: color 0.15s, background 0.15s;
  flex-shrink: 0;
}

.send-btn:hover,
.article-toggle-btn:hover {
  color: var(--text);
  background: var(--bg-light);
}

.send-btn:disabled,
.article-toggle-btn:disabled {
  opacity: 0.3;
  cursor: default;
}

.article-toggle-btn.active {
  color: var(--accent);
}

.input-bar.disabled #message-input {
  opacity: 0.5;
}

.input-bar.disabled .send-btn {
  opacity: 0.3;
  pointer-events: none;
}

.session-ended-message {
  text-align: center;
  color: var(--text-muted);
  font-size: 0.9rem;
  padding: 1rem;
}

/* ──────────────────────────────
   Exchange & Timeout Countdowns
   ────────────────────────────── */

.exchange-countdown,
.timeout-countdown {
  font-size: 0.8rem;
  color: var(--text-muted);
  text-align: center;
  padding: 0.25rem 0 0.5rem;
}

/* ──────────────────────────────
   Article View
   ────────────────────────────── */

.article-view {
  flex: 1;
  overflow-y: auto;
  padding: 3rem 1.5rem;
  padding-bottom: calc(var(--input-bar-height) + 2rem);
}

.article-content {
  max-width: 680px;
  margin: 0 auto;
}

.article-content h1 {
  font-size: 2.25rem;
  font-weight: 700;
  line-height: 1.2;
  margin-bottom: 0.5rem;
}

.article-domain {
  font-size: 0.85rem;
  color: var(--text-muted);
  margin-bottom: 2.5rem;
}

.article-content h2 {
  font-size: 1.5rem;
  font-weight: 700;
  line-height: 1.3;
  margin-top: 2.5rem;
  margin-bottom: 1rem;
}

.article-content h3 {
  font-size: 1.15rem;
  font-weight: 700;
  line-height: 1.4;
  margin-top: 2rem;
  margin-bottom: 0.75rem;
}

.article-content p {
  margin-bottom: 1.25rem;
  font-size: 1.05rem;
  line-height: 1.7;
}

.article-content blockquote {
  border-left: 3px solid var(--accent);
  padding-left: 1.25rem;
  margin: 1.5rem 0;
  color: var(--text-muted);
  font-style: italic;
}

.article-content ul,
.article-content ol {
  margin: 1rem 0 1.25rem 1.5rem;
}

.article-content li {
  margin-bottom: 0.5rem;
  line-height: 1.6;
}

.article-content hr {
  border: none;
  border-top: 1px solid var(--border);
  margin: 2.5rem 0;
}

.article-content a {
  color: var(--accent);
}

.article-footer {
  margin-top: 3rem;
  padding-top: 2rem;
  border-top: 1px solid var(--border);
  text-align: center;
}

.return-to-conversation {
  font-size: 0.9rem;
  color: var(--accent);
  background: none;
  border: 1px solid var(--accent);
  border-radius: 6px;
  padding: 0.6rem 1.25rem;
  cursor: pointer;
  transition: background 0.15s;
}

.return-to-conversation:hover {
  background: var(--accent-dim);
}

/* ──────────────────────────────
   Responsive — Mobile (≤ 768px)
   ────────────────────────────── */

@media (max-width: 768px) {
  .sidebar {
    display: none;
  }

  .mobile-header {
    display: flex;
  }

  .main-content {
    margin-left: 0;
    padding-top: 50px;
  }

  .input-bar {
    left: 0;
  }

  .hero-title {
    font-size: 2.25rem;
  }

  .hero-tagline {
    font-size: 1.05rem;
  }

  .concept-list-section {
    padding: 2.5rem 1rem 4rem;
  }

  .concept-card {
    padding: 1.25rem 1rem;
  }

  .chat-area {
    padding: 1.5rem 1rem;
  }

  .article-view {
    padding: 2rem 1rem;
    padding-bottom: calc(var(--input-bar-height) + 2rem);
  }

  .article-content h1 {
    font-size: 1.75rem;
  }
}