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

/* Light theme (default) */
:root {
  --bg: #f0f0f0;
  --surface: #ffffff;
  --border: #d8d8d8;
  --text: #2a2a2a;
  --dim: #777;
  --accent: #4a9eff;
  --green: #5cb85c;
  --orange: #e8883a;
  --red: #d9534f;
  --yellow: #c9a227;
  --mono: "SF Mono", "Fira Code", Menlo, Consolas, monospace;
  --panel-bar: #e8e8e8;
  --msg-tutor-bg: #f0f0f0;
  --msg-user-bg: #d6e6f7;
  --msg-user-border: #b0cceb;
  --drag-dot-hover: #555;
  --banner-bg: #fff3cd;
  --banner-text: #664d03;
}

/* Dark theme */
[data-theme="dark"] {
  --bg: #1a1a1a;
  --surface: #242424;
  --border: #3a3a3a;
  --text: #ddd;
  --dim: #888;
  --accent: #4a9eff;
  --green: #5cb85c;
  --orange: #e8883a;
  --red: #d9534f;
  --yellow: #c9a227;
  --panel-bar: #1e1e1e;
  --msg-tutor-bg: #2a2a2a;
  --msg-user-bg: #1a3a5c;
  --msg-user-border: #2a5a8c;
  --drag-dot-hover: #fff;
  --banner-bg: #c9a227;
  --banner-text: #000;
}

body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  background: var(--bg);
  color: var(--text);
  font-size: 14px;
  line-height: 1.5;
}

.hidden { display: none !important; }

/* Banner */
#proto-banner {
  background: var(--banner-bg);
  color: var(--banner-text);
  text-align: center;
  padding: 4px;
  font-size: 12px;
  font-weight: 600;
}

/* Header */
#header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 8px 16px;
  border-bottom: 1px solid var(--border);
  background: var(--surface);
}

.header-left { display: flex; align-items: center; gap: 10px; overflow: hidden; }

.header-flow {
  color: var(--dim);
  font-size: 12px;
  white-space: nowrap;
  margin-left: 6px;
}

.flow-arrow {
  color: var(--border);
  margin: 0 2px;
}

.logo {
  font-family: var(--mono);
  font-size: 15px;
  font-weight: 700;
  color: var(--accent);
}

.back-btn {
  background: none;
  border: 1px solid var(--border);
  color: var(--text);
  width: 28px;
  height: 28px;
  border-radius: 4px;
  cursor: pointer;
  font-size: 14px;
}

.theme-toggle {
  background: none;
  border: 1px solid var(--border);
  color: var(--dim);
  width: 28px;
  height: 28px;
  border-radius: 4px;
  cursor: pointer;
  font-size: 16px;
  display: flex;
  align-items: center;
  justify-content: center;
}

.theme-toggle:hover { color: var(--text); border-color: var(--dim); }

/* Views */
.view { max-width: 1300px; margin: 0 auto; padding: 16px; }

/* Home */

.lang-section { margin-bottom: 20px; }

.lang-header {
  font-family: var(--mono);
  font-size: 22px;
  font-weight: 700;
  color: var(--text);
  margin-bottom: 8px;
  padding-left: 2px;
}

.lang-row {
  display: flex;
  gap: 12px;
  overflow-x: auto;
  padding-bottom: 4px;
}

.lang-row .card {
  min-width: 230px;
  max-width: 280px;
  flex-shrink: 0;
}

.card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 6px;
  padding: 14px;
  cursor: pointer;
  position: relative;
}

.card:hover { border-color: var(--accent); }


.card-diff {
  font-size: 10px;
  text-transform: uppercase;
  color: var(--dim);
  font-weight: 600;
  letter-spacing: 0.5px;
}

.card h3 { font-size: 14px; margin: 4px 0 4px; }
.card p { color: var(--dim); font-size: 12px; line-height: 1.4; }

.card-badge {
  position: absolute;
  top: 8px;
  right: 8px;
  font-size: 10px;
  padding: 1px 6px;
  border-radius: 3px;
  font-weight: 600;
}

.card-badge.done { background: #5cb85c22; color: var(--green); border: 1px solid var(--green); }
.card-badge.revisit { background: #4a9eff15; color: var(--accent); border: 1px solid var(--accent); }

.proto-footer {
  text-align: center;
  color: var(--dim);
  font-size: 12px;
  font-style: italic;
  margin-top: 24px;
}

/* Lesson Layout */
.lesson-layout {
  display: grid;
  grid-template-columns: 1fr 6px 1fr;
  gap: 0;
  height: calc(100vh - 80px);
}

/* Drag Handle */
.drag-handle {
  cursor: col-resize;
  background: var(--border);
  position: relative;
  transition: background 0.15s;
}

.drag-handle:hover,
.drag-handle.dragging {
  background: var(--accent);
}

.drag-handle::after {
  content: "";
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  width: 2px;
  height: 32px;
  border-left: 1px solid var(--dim);
  border-right: 1px solid var(--dim);
  opacity: 0.4;
}

.drag-handle:hover::after,
.drag-handle.dragging::after {
  border-color: var(--drag-dot-hover);
  opacity: 0.7;
}

/* Code Panel */
.code-panel {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 6px;
  display: flex;
  flex-direction: column;
  overflow: hidden;
}

.panel-bar {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 2px 8px;
  border-bottom: 1px solid var(--border);
  background: var(--panel-bar);
}

.file-tabs { display: flex; gap: 1px; }

.file-tab {
  padding: 5px 10px;
  cursor: pointer;
  font-family: var(--mono);
  font-size: 12px;
  color: var(--dim);
  border-radius: 3px 3px 0 0;
}

.file-tab:hover { color: var(--text); }
.file-tab.active { color: var(--accent); background: var(--bg); }

.text-btn {
  background: none;
  border: none;
  color: var(--dim);
  font-size: 12px;
  cursor: pointer;
  font-family: var(--mono);
}

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

.code-panel pre {
  flex: 1;
  overflow: auto;
  margin: 0;
  padding: 0;
  font-size: 13px;
  line-height: 1.35;
}

.code-panel pre code,
.code-panel pre code.hljs {
  font-family: var(--mono);
  display: block;
  padding: 8px 12px 8px 0;
  line-height: 1.35 !important;
  font-size: 13px !important;
}

.ln {
  color: var(--dim);
  opacity: 0.35;
  margin-right: 1ch;
  user-select: none;
}

/* Chat Panel */
.chat-panel {
  display: flex;
  flex-direction: column;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 6px;
  overflow: hidden;
}

.phase-bar {
  display: flex;
  border-bottom: 1px solid var(--border);
  background: var(--panel-bar);
}

.phase {
  flex: 1;
  padding: 6px 8px;
  text-align: center;
  font-size: 11px;
  font-weight: 600;
  text-transform: lowercase;
  color: var(--dim);
  border-bottom: 2px solid transparent;
}

.phase.active { color: var(--accent); border-bottom-color: var(--accent); }
.phase.done { color: var(--green); border-bottom-color: var(--green); }

/* Explore */
.phase-content { flex: 1; overflow: auto; display: flex; flex-direction: column; }
.phase-content.hidden { display: none !important; }

.explore-intro { padding: 14px 14px 8px; }
.explore-intro p { font-size: 13px; margin-bottom: 6px; }

.small { font-size: 12px; }
.dim { color: var(--dim); }

.seeds { padding: 0 14px 8px; }

.seed {
  display: inline-block;
  background: var(--bg);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 3px 10px;
  margin: 2px 3px;
  font-size: 12px;
  color: var(--accent);
  cursor: pointer;
}

.seed:hover { border-color: var(--accent); }

#user-questions {
  margin: 0 14px 8px;
  padding: 8px 10px;
  background: var(--bg);
  border: 1px solid var(--border);
  border-radius: 4px;
  color: var(--text);
  font-family: inherit;
  font-size: 13px;
  resize: vertical;
  min-height: 60px;
}

#user-questions:focus { outline: none; border-color: var(--accent); }

.actions { padding: 0 14px 14px; display: flex; gap: 6px; align-items: center; }

/* Language select */
#lang-select {
  background: var(--bg);
  color: var(--text);
  border: 1px solid var(--border);
  border-radius: 4px;
  font-size: 12px;
  padding: 5px 8px;
  cursor: pointer;
}

#lang-select:focus {
  outline: none;
  border-color: var(--accent);
}

/* Mode toggle */
.mode-toggle {
  display: flex;
  border: 1px solid var(--border);
  border-radius: 4px;
  overflow: hidden;
}

.mode-opt {
  background: none;
  border: none;
  color: var(--dim);
  font-size: 12px;
  font-weight: 600;
  padding: 5px 12px;
  cursor: pointer;
  transition: all 0.15s;
}

.mode-opt:first-child { border-right: 1px solid var(--border); }

.mode-opt.active {
  background: var(--accent);
  color: #fff;
}

.btn-primary {
  background: var(--accent);
  color: #fff;
  border: none;
  padding: 7px 16px;
  border-radius: 4px;
  cursor: pointer;
  font-size: 13px;
  font-weight: 600;
}

.btn-primary:hover { filter: brightness(1.1); }
.btn-primary:disabled { opacity: 0.4; cursor: default; }

.btn-secondary {
  background: var(--surface);
  color: var(--dim);
  border: 1px solid var(--border);
  padding: 7px 14px;
  border-radius: 4px;
  cursor: pointer;
  font-size: 13px;
}

.btn-secondary:hover { color: var(--text); border-color: var(--dim); }

/* Exchange bar */
.exchange-bar {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 4px 12px;
  background: var(--panel-bar);
  border-bottom: 1px solid var(--border);
  font-size: 11px;
  color: var(--dim);
}


/* Messages */
.messages {
  flex: 1;
  overflow-y: auto;
  padding: 12px;
  display: flex;
  flex-direction: column;
  gap: 8px;
}

.msg {
  max-width: 85%;
  padding: 8px 10px;
  border-radius: 6px;
  font-size: 13px;
  line-height: 1.45;
  white-space: pre-wrap;
  word-wrap: break-word;
}

.msg-tutor { align-self: flex-start; background: var(--msg-tutor-bg); border: 1px solid var(--border); }
.msg-user { align-self: flex-end; background: var(--msg-user-bg); border: 1px solid var(--msg-user-border); }
.msg-system { align-self: center; color: var(--dim); font-size: 12px; font-style: italic; }

.msg code { font-family: var(--mono); background: var(--bg); padding: 1px 4px; border-radius: 2px; font-size: 12px; }
.msg pre { background: var(--bg); padding: 6px 8px; border-radius: 3px; margin: 4px 0; overflow-x: auto; }
.msg pre code { background: none; padding: 0; }

.msg-label { font-size: 10px; color: var(--accent); font-weight: 600; text-transform: uppercase; margin-bottom: 3px; }

.challenge-label {
  align-self: center;
  color: var(--orange);
  font-size: 11px;
  font-weight: 700;
  text-transform: uppercase;
  padding: 3px 12px;
  border: 1px solid var(--orange);
  border-radius: 3px;
}

.typing { align-self: flex-start; color: var(--dim); font-style: italic; font-size: 12px; padding: 6px; }

.input-row {
  padding: 8px 12px;
  border-top: 1px solid var(--border);
  display: flex;
  gap: 6px;
  align-items: flex-end;
}

#chat-input {
  flex: 1;
  padding: 7px 10px;
  background: var(--bg);
  border: 1px solid var(--border);
  border-radius: 4px;
  color: var(--text);
  font-family: inherit;
  font-size: 13px;
  resize: none;
  max-height: 100px;
}

#chat-input:focus { outline: none; border-color: var(--accent); }

/* Completion */
.completion { padding: 24px 16px; text-align: center; }
.completion h2 { font-size: 18px; color: var(--green); margin-bottom: 4px; }
.completion .concepts { display: flex; flex-wrap: wrap; gap: 6px; justify-content: center; margin: 12px 0; }
.completion .tag { font-size: 12px; padding: 2px 10px; border-radius: 3px; background: #5cb85c22; color: var(--green); border: 1px solid var(--green); }
.completion .summary { color: var(--dim); font-size: 13px; max-width: 460px; margin: 12px auto; text-align: left; line-height: 1.5; }
.completion .revisit-note { font-size: 12px; color: var(--accent); margin: 16px auto; max-width: 400px; padding: 8px 12px; border: 1px solid var(--border); border-radius: 4px; }
.completion .comp-actions { display: flex; gap: 6px; justify-content: center; margin-top: 16px; }

/* Confetti */
#confetti { position: fixed; top: 0; left: 0; width: 100%; height: 100%; pointer-events: none; z-index: 200; overflow: hidden; }
.confetti-bit { position: absolute; width: 6px; height: 6px; top: -8px; border-radius: 1px; animation: fall 2.5s ease-in forwards; }
@keyframes fall { to { transform: translateY(100vh) rotate(720deg); opacity: 0; } }

/* Toast */
.toast {
  position: fixed;
  bottom: 16px;
  left: 50%;
  transform: translateX(-50%);
  background: var(--surface);
  border: 1px solid var(--green);
  color: var(--green);
  padding: 6px 16px;
  border-radius: 4px;
  font-size: 13px;
  z-index: 999;
}

.toast.hidden { opacity: 0; pointer-events: none; }

/* I Know chips */
.i-know {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 8px;
  margin-bottom: 16px;
}

.i-know-label {
  color: var(--dim);
  font-size: 13px;
}

.i-know-chips {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 6px;
}

.chip-row {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: 6px;
}

.i-know-chip {
  padding: 3px 12px;
  border-radius: 14px;
  font-size: 12px;
  font-weight: 500;
  cursor: pointer;
  border: 1px solid var(--border);
  background: var(--surface);
  color: var(--dim);
  transition: all 0.15s;
  user-select: none;
}

.i-know-chip:hover {
  border-color: var(--accent);
  color: var(--text);
}

.i-know-chip.active {
  border-color: var(--accent);
  background: rgba(74, 158, 255, 0.12);
  color: var(--accent);
}

@media (max-width: 900px) {
  .lesson-layout { grid-template-columns: 1fr; height: auto; }
  .drag-handle { display: none; }
  .code-panel { max-height: 40vh; }
  .chat-panel { min-height: 50vh; }
}