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

body {
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
  background: #F0F4FF;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  align-items: center;
}

.hidden {
  display: none !important;
}

/* ── Password screen ───────────────────────────────────────── */
#password-screen {
  width: 100%;
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 24px 16px;
}

.error-msg {
  color: #DC2626;
  font-size: 0.85rem;
  text-align: center;
  width: 100%;
}

.form-group input[type="password"] {
  width: 100%;
  padding: 11px 14px;
  border: 2px solid #CBD5E1;
  border-radius: 10px;
  font-size: 0.93rem;
  font-family: inherit;
  outline: none;
  transition: border-color 0.2s;
  color: #1E293B;
}

.form-group input[type="password"]:focus {
  border-color: #1D4ED8;
}

.form-group input[type="password"]::placeholder {
  color: #94A3B8;
}

/* ── Start screen ──────────────────────────────────────────── */
#start-screen {
  width: 100%;
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 24px 16px;
}

.start-card {
  background: white;
  border-radius: 20px;
  padding: 40px 36px;
  width: 100%;
  max-width: 520px;
  box-shadow: 0 4px 24px rgba(0,0,0,0.09);
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 20px;
}

.start-icon {
  font-size: 3rem;
  line-height: 1;
}

.start-card h1 {
  font-size: 1.6rem;
  font-weight: 800;
  color: #1E293B;
  text-align: center;
  line-height: 1.3;
}

.start-desc {
  color: #64748B;
  font-size: 0.92rem;
  text-align: center;
  line-height: 1.6;
  max-width: 380px;
}

.form-group {
  width: 100%;
  display: flex;
  flex-direction: column;
  gap: 6px;
}

.form-group label {
  font-size: 0.88rem;
  font-weight: 600;
  color: #334155;
}

.form-group textarea,
.form-group input[type="text"] {
  width: 100%;
  padding: 11px 14px;
  border: 2px solid #CBD5E1;
  border-radius: 10px;
  font-size: 0.93rem;
  font-family: inherit;
  outline: none;
  resize: none;
  transition: border-color 0.2s;
  line-height: 1.5;
  color: #1E293B;
}

.form-group textarea:focus,
.form-group input[type="text"]:focus {
  border-color: #1D4ED8;
}

.form-group textarea::placeholder,
.form-group input::placeholder {
  color: #94A3B8;
}

.hint {
  font-size: 0.78rem;
  color: #94A3B8;
}

/* ── Mode tabs ─────────────────────────────────────────────── */
.mode-tabs {
  display: flex;
  width: 100%;
  background: #F1F5F9;
  border-radius: 10px;
  padding: 4px;
  gap: 4px;
}

.tab-btn {
  flex: 1;
  padding: 9px;
  border: none;
  background: transparent;
  border-radius: 8px;
  font-size: 0.88rem;
  font-weight: 600;
  color: #64748B;
  cursor: pointer;
  transition: background 0.2s, color 0.2s;
}

.tab-btn.active {
  background: white;
  color: #1D4ED8;
  box-shadow: 0 1px 3px rgba(0,0,0,0.1);
}

/* ── Topic select ──────────────────────────────────────────── */
.form-group select {
  width: 100%;
  padding: 11px 14px;
  border: 2px solid #CBD5E1;
  border-radius: 10px;
  font-size: 0.93rem;
  font-family: inherit;
  outline: none;
  background: white;
  color: #1E293B;
  cursor: pointer;
  transition: border-color 0.2s;
  appearance: none;
  background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='16' height='16' viewBox='0 0 24 24' fill='none' stroke='%2364748B' stroke-width='2'%3E%3Cpolyline points='6 9 12 15 18 9'%3E%3C/polyline%3E%3C/svg%3E");
  background-repeat: no-repeat;
  background-position: right 12px center;
  padding-right: 36px;
}

.form-group select:focus {
  border-color: #1D4ED8;
}

/* ── Start button (shared) ─────────────────────────────────── */
.start-btn {
  width: 100%;
  padding: 13px;
  background: #1D4ED8;
  color: white;
  border: none;
  border-radius: 12px;
  font-size: 1rem;
  font-weight: 700;
  cursor: pointer;
  transition: background 0.2s, opacity 0.2s;
  margin-top: 4px;
}

.start-btn:hover:not(:disabled) {
  background: #1E40AF;
}

.start-btn:disabled {
  opacity: 0.45;
  cursor: not-allowed;
}

/* ── Question divider in chat ──────────────────────────────── */
.question-divider {
  text-align: center;
  color: #94A3B8;
  font-size: 0.78rem;
  padding: 8px 0;
  letter-spacing: 0.5px;
}

/* ── Chat screen ───────────────────────────────────────────── */
#chat-screen {
  width: 100%;
  height: 100vh;
  display: flex;
  flex-direction: column;
  align-items: center;
}

header {
  width: 100%;
  background: #1D4ED8;
  color: white;
  padding: 14px 24px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  box-shadow: 0 2px 8px rgba(0,0,0,0.15);
  flex-shrink: 0;
}

.header-left {
  display: flex;
  align-items: center;
  gap: 12px;
}

.header-icon {
  font-size: 1.8rem;
  line-height: 1;
}

.header-title {
  font-size: 1rem;
  font-weight: 700;
}

.subtitle {
  font-size: 0.72rem;
  opacity: 0.75;
  margin-top: 1px;
}

.header-right {
  display: flex;
  gap: 8px;
  align-items: center;
}

.header-btn {
  background: rgba(255,255,255,0.18);
  border: 1px solid rgba(255,255,255,0.35);
  color: white;
  padding: 7px 14px;
  border-radius: 8px;
  cursor: pointer;
  font-size: 0.82rem;
  font-weight: 600;
  transition: background 0.2s;
  white-space: nowrap;
}

.header-btn:hover {
  background: rgba(255,255,255,0.28);
}

/* ── Score badge ───────────────────────────────────────────── */
.score-badge {
  background: rgba(255,255,255,0.15);
  border: 1px solid rgba(255,255,255,0.3);
  color: rgba(255,255,255,0.7);
  padding: 7px 14px;
  border-radius: 8px;
  font-size: 0.82rem;
  font-weight: 600;
  white-space: nowrap;
  transition: background 0.3s, color 0.3s, border-color 0.3s;
}

.score-badge--nonzero {
  background: rgba(34,197,94,0.25);
  border-color: rgba(34,197,94,0.5);
  color: #86EFAC;
}

/* ── Chat body ─────────────────────────────────────────────── */
.chat-wrapper {
  width: 100%;
  max-width: 780px;
  flex: 1;
  display: flex;
  flex-direction: column;
  padding: 0 16px;
  overflow: hidden;
}

#chat-box {
  flex: 1;
  overflow-y: auto;
  padding: 24px 0 16px;
  display: flex;
  flex-direction: column;
  gap: 14px;
  scroll-behavior: smooth;
}

/* ── Messages ──────────────────────────────────────────────── */
.message {
  display: flex;
  align-items: flex-end;
  gap: 10px;
  max-width: 88%;
  animation: fadeUp 0.22s ease;
}

@keyframes fadeUp {
  from { opacity: 0; transform: translateY(8px); }
  to   { opacity: 1; transform: translateY(0); }
}

.message.tutor   { align-self: flex-start; }
.message.student { align-self: flex-end; flex-direction: row-reverse; }

.avatar {
  width: 34px;
  height: 34px;
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.1rem;
  flex-shrink: 0;
}

.tutor   .avatar { background: #DBEAFE; }
.student .avatar { background: #D1FAE5; }

.bubble {
  padding: 12px 16px;
  border-radius: 16px;
  font-size: 0.93rem;
  line-height: 1.6;
  max-width: 100%;
  word-wrap: break-word;
}

.tutor .bubble {
  background: white;
  color: #1E293B;
  border-bottom-left-radius: 4px;
  box-shadow: 0 1px 4px rgba(0,0,0,0.08);
}

.student .bubble {
  background: #1D4ED8;
  color: white;
  border-bottom-right-radius: 4px;
}

/* ── Typing indicator ──────────────────────────────────────── */
.typing-indicator {
  display: flex;
  align-items: center;
  gap: 10px;
  align-self: flex-start;
}

.typing-indicator .avatar { background: #DBEAFE; }

.dots {
  display: flex;
  gap: 5px;
  background: white;
  padding: 12px 16px;
  border-radius: 16px;
  border-bottom-left-radius: 4px;
  box-shadow: 0 1px 4px rgba(0,0,0,0.08);
}

.dots span {
  width: 8px;
  height: 8px;
  background: #93C5FD;
  border-radius: 50%;
  animation: bounce 1.2s infinite;
}

.dots span:nth-child(2) { animation-delay: 0.2s; }
.dots span:nth-child(3) { animation-delay: 0.4s; }

@keyframes bounce {
  0%, 60%, 100% { transform: translateY(0); }
  30%            { transform: translateY(-6px); }
}

/* ── Input area ────────────────────────────────────────────── */
.input-area {
  padding: 12px 0 20px;
  display: flex;
  gap: 10px;
  align-items: flex-end;
  flex-shrink: 0;
}

#user-input {
  flex: 1;
  padding: 12px 16px;
  border: 2px solid #CBD5E1;
  border-radius: 12px;
  font-size: 0.93rem;
  resize: none;
  outline: none;
  font-family: inherit;
  line-height: 1.5;
  max-height: 140px;
  background: white;
  transition: border-color 0.2s;
  color: #1E293B;
}

#user-input:focus { border-color: #1D4ED8; }
#user-input::placeholder { color: #94A3B8; }

#send-btn {
  background: #1D4ED8;
  border: none;
  color: white;
  width: 46px;
  height: 46px;
  border-radius: 12px;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: background 0.2s, transform 0.1s;
  flex-shrink: 0;
}

#send-btn:hover:not(:disabled) { background: #1E40AF; }
#send-btn:active               { transform: scale(0.95); }
#send-btn:disabled             { background: #93C5FD; cursor: not-allowed; }
#send-btn svg                  { width: 20px; height: 20px; }