:root {
  --color-bg: #0A0A0A;
  --color-surface: #1A1A1A;
  --color-surface-hover: #252525;
  --color-primary: #6366F1;
  --color-primary-hover: #4F46E5;
  --color-text: #F5F5F5;
  --color-text-muted: #9CA3AF;
  --color-border: #2D2D2D;
  --color-user-msg: #1E3A8A;
  --color-assistant-msg: #1A1A1A;
  --radius: 12px;
  --radius-sm: 8px;
  --shadow: 0 4px 12px rgba(0,0,0,0.3);
  --transition: all 0.2s ease;
}

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

body {
  font-family: 'Inter', -apple-system, BlinkMacSystemFont, sans-serif;
  background: var(--color-bg);
  color: var(--color-text);
  line-height: 1.6;
  height: 100vh;
  overflow: hidden;
}

/* Auth Modal */
.modal {
  position: fixed;
  inset: 0;
  z-index: 1000;
  display: flex;
  align-items: center;
  justify-content: center;
}
.modal.hidden { display: none; }
.modal-overlay {
  position: absolute;
  inset: 0;
  background: rgba(0,0,0,0.7);
  backdrop-filter: blur(4px);
}
.modal-content {
  position: relative;
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  padding: 32px;
  width: 100%;
  max-width: 400px;
  box-shadow: var(--shadow);
}
.modal-close {
  position: absolute;
  top: 16px;
  right: 16px;
  background: none;
  border: none;
  color: var(--color-text-muted);
  font-size: 24px;
  cursor: pointer;
  transition: var(--transition);
}
.modal-close:hover { color: var(--color-text); }
.auth-tabs {
  display: flex;
  gap: 16px;
  margin-bottom: 24px;
  border-bottom: 1px solid var(--color-border);
  padding-bottom: 16px;
}
.auth-tab {
  background: none;
  border: none;
  color: var(--color-text-muted);
  font-size: 16px;
  font-weight: 500;
  cursor: pointer;
  padding: 8px 0;
  transition: var(--transition);
}
.auth-tab.active { color: var(--color-primary); border-bottom: 2px solid var(--color-primary); }
.auth-form { display: flex; flex-direction: column; gap: 20px; }
.form-group label {
  display: block;
  margin-bottom: 8px;
  font-size: 14px;
  color: var(--color-text-muted);
}
.form-group input {
  width: 100%;
  padding: 12px 16px;
  background: var(--color-bg);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-sm);
  color: var(--color-text);
  font-size: 16px;
  transition: var(--transition);
}
.form-group input:focus {
  outline: none;
  border-color: var(--color-primary);
  box-shadow: 0 0 0 3px rgba(99, 102, 241, 0.15);
}
.btn-primary {
  background: var(--color-primary);
  color: white;
  border: none;
  border-radius: var(--radius-sm);
  padding: 12px 24px;
  font-size: 16px;
  font-weight: 600;
  cursor: pointer;
  transition: var(--transition);
}
.btn-primary:hover { background: var(--color-primary-hover); }
.btn-primary:disabled {
  opacity: 0.6;
  cursor: not-allowed;
}
.btn-full { width: 100%; }
.auth-error {
  color: #EF4444;
  font-size: 14px;
  text-align: center;
  margin-top: -8px;
}

/* App Layout */
.app {
  display: flex;
  height: 100vh;
}

/* Sidebar */
.sidebar {
  width: 260px;
  background: var(--color-surface);
  border-right: 1px solid var(--color-border);
  display: flex;
  flex-direction: column;
  transition: transform 0.3s ease;
}
.sidebar-header {
  padding: 20px;
  border-bottom: 1px solid var(--color-border);
}
.logo {
  font-size: 20px;
  font-weight: 700;
  margin-bottom: 20px;
  background: linear-gradient(135deg, var(--color-primary), #A855F7);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
}
.btn-new-chat {
  display: flex;
  align-items: center;
  gap: 8px;
  width: 100%;
  padding: 12px 16px;
  background: var(--color-bg);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-sm);
  color: var(--color-text);
  font-size: 14px;
  font-weight: 500;
  cursor: pointer;
  transition: var(--transition);
}
.btn-new-chat:hover {
  background: var(--color-surface-hover);
  border-color: var(--color-primary);
}
.conversation-list {
  flex: 1;
  overflow-y: auto;
  padding: 12px;
}
.conversation-item {
  padding: 12px 16px;
  border-radius: var(--radius-sm);
  cursor: pointer;
  margin-bottom: 4px;
  transition: var(--transition);
  color: var(--color-text);
  font-size: 14px;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}
.conversation-item:hover { background: var(--color-surface-hover); }
.conversation-item.active { background: var(--color-primary); color: white; }
.conversation-item .delete-btn {
  float: right;
  opacity: 0;
  background: none;
  border: none;
  color: inherit;
  cursor: pointer;
  padding: 2px;
}
.conversation-item:hover .delete-btn { opacity: 0.6; }
.conversation-item .delete-btn:hover { opacity: 1; color: #EF4444; }
.sidebar-footer {
  padding: 16px;
  border-top: 1px solid var(--color-border);
  display: flex;
  align-items: center;
  justify-content: space-between;
}
.user-info {
  display: flex;
  align-items: center;
  gap: 12px;
}
.user-avatar {
  width: 32px;
  height: 32px;
  border-radius: 50%;
  background: var(--color-primary);
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: 600;
  font-size: 14px;
}
.user-name {
  font-size: 14px;
  font-weight: 500;
}
.btn-logout {
  background: none;
  border: none;
  color: var(--color-text-muted);
  font-size: 14px;
  cursor: pointer;
  transition: var(--transition);
}
.btn-logout:hover { color: var(--color-text); }

/* Main Chat */
.main {
  flex: 1;
  display: flex;
  flex-direction: column;
  overflow: hidden;
}
.chat-container {
  display: flex;
  flex-direction: column;
  height: 100%;
}
.chat-messages {
  flex: 1;
  overflow-y: auto;
  padding: 24px;
  display: flex;
  flex-direction: column;
  gap: 24px;
}
.message {
  display: flex;
  gap: 16px;
  max-width: 800px;
  margin: 0 auto;
  width: 100%;
  animation: fadeUp 0.3s ease;
}
.message.user { flex-direction: row-reverse; }
.message-avatar {
  width: 36px;
  height: 36px;
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: 600;
  font-size: 14px;
  flex-shrink: 0;
}
.message.user .message-avatar {
  background: var(--color-primary);
  color: white;
}
.message.assistant .message-avatar {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  color: var(--color-text);
}
.message-content {
  padding: 16px 20px;
  border-radius: var(--radius);
  line-height: 1.6;
  font-size: 15px;
  max-width: 80%;
}
.message.user .message-content {
  background: var(--color-user-msg);
  border-bottom-right-radius: 4px;
}
.message.assistant .message-content {
  background: var(--color-assistant-msg);
  border: 1px solid var(--color-border);
  border-bottom-left-radius: 4px;
}
.message-content p { margin-bottom: 8px; }
.message-content p:last-child { margin-bottom: 0; }
.message-content code {
  background: rgba(0,0,0,0.3);
  padding: 2px 6px;
  border-radius: 4px;
  font-family: 'SF Mono', Monaco, monospace;
  font-size: 13px;
}
.message-content pre {
  background: rgba(0,0,0,0.4);
  padding: 16px;
  border-radius: var(--radius-sm);
  overflow-x: auto;
  margin: 12px 0;
}
.message-content pre code {
  background: none;
  padding: 0;
}

/* Input Area */
.chat-input-area {
  padding: 16px 24px 24px;
  border-top: 1px solid var(--color-border);
  background: var(--color-bg);
}
.chat-form {
  max-width: 800px;
  margin: 0 auto;
}
.input-wrapper {
  display: flex;
  gap: 12px;
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  padding: 12px 16px;
  transition: var(--transition);
}
.input-wrapper:focus-within {
  border-color: var(--color-primary);
  box-shadow: 0 0 0 3px rgba(99, 102, 241, 0.15);
}
#message-input {
  flex: 1;
  background: transparent;
  border: none;
  color: var(--color-text);
  font-size: 16px;
  font-family: inherit;
  resize: none;
  max-height: 200px;
  line-height: 1.5;
}
#message-input:focus { outline: none; }
.btn-send {
  width: 40px;
  height: 40px;
  border-radius: 50%;
  background: var(--color-primary);
  border: none;
  color: white;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: var(--transition);
}
.btn-send:hover:not(:disabled) { background: var(--color-primary-hover); }
.btn-send:disabled {
  background: var(--color-surface-hover);
  color: var(--color-text-muted);
  cursor: not-allowed;
}
.input-hint {
  text-align: center;
  font-size: 12px;
  color: var(--color-text-muted);
  margin-top: 8px;
}

/* Animations */
@keyframes fadeUp {
  from { opacity: 0; transform: translateY(12px); }
  to { opacity: 1; transform: translateY(0); }
}

/* Scrollbar */
::-webkit-scrollbar { width: 8px; }
::-webkit-scrollbar-track { background: transparent; }
::-webkit-scrollbar-thumb { background: var(--color-border); border-radius: 4px; }
::-webkit-scrollbar-thumb:hover { background: var(--color-text-muted); }

/* Responsive */
@media (max-width: 768px) {
  .sidebar {
    position: fixed;
    left: 0;
    top: 0;
    bottom: 0;
    z-index: 100;
    transform: translateX(-100%);
  }
  .sidebar.open { transform: translateX(0); }
  .main { margin-left: 0; }
  .mobile-menu-btn {
    display: block;
    position: fixed;
    top: 16px;
    left: 16px;
    z-index: 101;
    background: var(--color-surface);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-sm);
    padding: 8px;
    cursor: pointer;
  }
}
@media (min-width: 769px) {
  .mobile-menu-btn { display: none; }
}