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

:root {
    --bg-primary: #0f1117;
    --bg-secondary: #1a1d29;
    --bg-tertiary: #252936;
    --bg-hover: #2d3142;
    --text-primary: #e1e4e8;
    --text-secondary: #8b8d98;
    --text-muted: #6e7179;
    --accent: #6366f1;
    --accent-hover: #5558e0;
    --border: #2d3142;
    --success: #10b981;
    --error: #ef4444;
    --shadow: rgba(0, 0, 0, 0.3);
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Roboto', 'Oxygen', 'Ubuntu', sans-serif;
    background: var(--bg-primary);
    color: var(--text-primary);
    min-height: 100vh;
    overflow: hidden;
}

/* Screens */
.screen {
    display: none;
    width: 100%;
    height: 100vh;
}

.screen.active {
    display: flex;
}

/* Login Screen */
.login-container {
    width: 100%;
    max-width: 420px;
    margin: auto;
    padding: 20px;
}

.login-content {
    background: var(--bg-secondary);
    padding: 48px 40px;
    border-radius: 16px;
    border: 1px solid var(--border);
    box-shadow: 0 4px 24px var(--shadow);
}

.login-logo {
    font-size: 4rem;
    text-align: center;
    margin-bottom: 16px;
}

.login-content h1 {
    font-size: 2rem;
    font-weight: 600;
    text-align: center;
    margin-bottom: 8px;
    color: var(--text-primary);
}

.subtitle {
    text-align: center;
    color: var(--text-secondary);
    margin-bottom: 32px;
    font-size: 0.95rem;
}

.input-group {
    margin-bottom: 16px;
}

.input-group input {
    width: 100%;
    padding: 14px 16px;
    background: var(--bg-tertiary);
    border: 1px solid var(--border);
    border-radius: 10px;
    color: var(--text-primary);
    font-size: 0.95rem;
    transition: all 0.2s ease;
}

.input-group input:focus {
    outline: none;
    border-color: var(--accent);
    box-shadow: 0 0 0 3px rgba(99, 102, 241, 0.1);
}

.btn-primary {
    width: 100%;
    padding: 14px;
    background: var(--accent);
    border: none;
    border-radius: 10px;
    color: white;
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    margin-top: 8px;
    transition: all 0.2s ease;
}

.btn-primary:hover {
    background: var(--accent-hover);
    transform: translateY(-1px);
}

.btn-primary:active {
    transform: translateY(0);
}

.error-message {
    color: var(--error);
    font-size: 0.9rem;
    margin-top: 16px;
    text-align: center;
    min-height: 20px;
}

/* App Container */
.app-container {
    display: flex;
    width: 100%;
    height: 100vh;
    background: var(--bg-primary);
}

/* Sidebar */
.sidebar {
    width: 280px;
    background: var(--bg-secondary);
    border-right: 1px solid var(--border);
    display: flex;
    flex-direction: column;
    transition: all 0.3s ease;
}

.sidebar.collapsed {
    width: 0;
    overflow: hidden;
}

.sidebar-header {
    padding: 20px;
    border-bottom: 1px solid var(--border);
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.sidebar-header h2 {
    font-size: 1.1rem;
    font-weight: 600;
    color: var(--text-primary);
}

.btn-icon {
    background: transparent;
    border: none;
    color: var(--text-secondary);
    padding: 8px;
    border-radius: 8px;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: all 0.2s ease;
}

.btn-icon:hover {
    background: var(--bg-hover);
    color: var(--text-primary);
}

.chat-list {
    flex: 1;
    overflow-y: auto;
    padding: 8px;
}

.chat-list::-webkit-scrollbar {
    width: 6px;
}

.chat-list::-webkit-scrollbar-track {
    background: transparent;
}

.chat-list::-webkit-scrollbar-thumb {
    background: var(--border);
    border-radius: 3px;
}

.chat-item {
    display: flex;
    align-items: center;
    gap: 8px;
    padding: 12px;
    margin-bottom: 4px;
    border-radius: 10px;
    cursor: pointer;
    transition: all 0.2s ease;
    position: relative;
}

.chat-item:hover {
    background: var(--bg-hover);
}

.chat-item.active {
    background: var(--bg-tertiary);
}

.chat-item-content {
    flex: 1;
    min-width: 0;
}

.chat-title {
    font-size: 0.95rem;
    font-weight: 500;
    color: var(--text-primary);
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
    margin-bottom: 2px;
}

.chat-preview {
    font-size: 0.85rem;
    color: var(--text-muted);
}

.delete-chat-btn {
    background: transparent;
    border: none;
    color: var(--text-muted);
    padding: 6px;
    border-radius: 6px;
    cursor: pointer;
    opacity: 0;
    transition: all 0.2s ease;
}

.chat-item:hover .delete-chat-btn {
    opacity: 1;
}

.delete-chat-btn:hover {
    background: var(--error);
    color: white;
}

/* Main Area */
.main-area {
    flex: 1;
    display: flex;
    flex-direction: column;
    min-width: 0;
}

.chat-header {
    padding: 16px 20px;
    border-bottom: 1px solid var(--border);
    display: flex;
    align-items: center;
    gap: 16px;
    background: var(--bg-secondary);
}

.header-title {
    flex: 1;
    min-width: 0;
}

.header-title h1 {
    font-size: 1.25rem;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: 2px;
}

.status {
    font-size: 0.85rem;
    color: var(--text-secondary);
}

/* Chat Messages */
.chat-messages {
    flex: 1;
    overflow-y: auto;
    padding: 24px;
    display: flex;
    flex-direction: column;
    gap: 16px;
}

.chat-messages::-webkit-scrollbar {
    width: 8px;
}

.chat-messages::-webkit-scrollbar-track {
    background: transparent;
}

.chat-messages::-webkit-scrollbar-thumb {
    background: var(--border);
    border-radius: 4px;
}

.welcome-message {
    text-align: center;
    padding: 60px 20px;
    color: var(--text-secondary);
}

.welcome-message h2 {
    font-size: 1.75rem;
    margin-bottom: 12px;
    color: var(--text-primary);
}

.welcome-message p {
    font-size: 1.05rem;
}

.message {
    display: flex;
    gap: 12px;
    animation: slideUp 0.3s ease;
}

@keyframes slideUp {
    from {
        opacity: 0;
        transform: translateY(10px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.message-avatar {
    width: 36px;
    height: 36px;
    border-radius: 50%;
    background: var(--bg-tertiary);
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 1.25rem;
    flex-shrink: 0;
}

.message-content {
    flex: 1;
    padding: 12px 16px;
    border-radius: 12px;
    line-height: 1.6;
    min-width: 0;
}

.user-message .message-content {
    background: var(--accent);
    color: white;
}

.assistant-message .message-content {
    background: var(--bg-secondary);
    border: 1px solid var(--border);
}

.error-message .message-content {
    background: var(--bg-secondary);
    border: 1px solid var(--error);
    color: var(--error);
}

.message-content p {
    margin-bottom: 12px;
}

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

.message-content h1,
.message-content h2,
.message-content h3 {
    margin: 16px 0 8px;
    color: var(--text-primary);
}

.message-content h1 {
    font-size: 1.5rem;
}

.message-content h2 {
    font-size: 1.25rem;
}

.message-content h3 {
    font-size: 1.1rem;
}

.message-content strong {
    font-weight: 600;
}

.message-content code {
    background: var(--bg-tertiary);
    padding: 2px 6px;
    border-radius: 4px;
    font-family: 'Monaco', 'Courier New', monospace;
    font-size: 0.9em;
}

.message-content pre {
    background: var(--bg-tertiary);
    padding: 16px;
    border-radius: 8px;
    overflow-x: auto;
    margin: 12px 0;
    border: 1px solid var(--border);
}

.message-content pre code {
    background: none;
    padding: 0;
}

.message-content ul,
.message-content ol {
    margin: 12px 0;
    padding-left: 24px;
}

.message-content li {
    margin: 6px 0;
}

.message-content a {
    color: var(--accent);
    text-decoration: underline;
}

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

/* KaTeX */
.katex {
    font-size: 1.1em;
}

.katex-display {
    margin: 16px 0;
}

/* Typing Indicator */
.typing-indicator {
    display: flex;
    gap: 6px;
    padding: 8px 0;
}

.typing-indicator span {
    width: 8px;
    height: 8px;
    background: var(--text-muted);
    border-radius: 50%;
    animation: bounce 1.4s infinite;
}

.typing-indicator span:nth-child(2) {
    animation-delay: 0.2s;
}

.typing-indicator span:nth-child(3) {
    animation-delay: 0.4s;
}

@keyframes bounce {
    0%, 60%, 100% {
        transform: translateY(0);
        opacity: 0.5;
    }
    30% {
        transform: translateY(-10px);
        opacity: 1;
    }
}

/* Chat Input */
.chat-input-container {
    padding: 20px;
    background: var(--bg-secondary);
    border-top: 1px solid var(--border);
}

.input-wrapper {
    display: flex;
    align-items: flex-end;
    gap: 12px;
    background: var(--bg-tertiary);
    border: 1px solid var(--border);
    border-radius: 12px;
    padding: 12px;
    transition: all 0.2s ease;
}

.input-wrapper:focus-within {
    border-color: var(--accent);
    box-shadow: 0 0 0 3px rgba(99, 102, 241, 0.1);
}

#user-input {
    flex: 1;
    background: transparent;
    border: none;
    color: var(--text-primary);
    font-size: 0.95rem;
    resize: none;
    outline: none;
    font-family: inherit;
    line-height: 1.5;
}

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

.btn-send {
    background: var(--accent);
    border: none;
    color: white;
    padding: 10px;
    border-radius: 8px;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: all 0.2s ease;
    flex-shrink: 0;
}

.btn-send:hover:not(:disabled) {
    background: var(--accent-hover);
    transform: scale(1.05);
}

.btn-send:disabled {
    opacity: 0.5;
    cursor: not-allowed;
}

/* Mobile Overlay */
.sidebar-overlay {
    display: none;
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(0, 0, 0, 0.5);
    z-index: 99;
    backdrop-filter: blur(2px);
}

.sidebar-overlay.active {
    display: block;
}

/* Mobile Responsive */
@media (max-width: 768px) {
    .sidebar {
        position: fixed;
        left: 0;
        top: 0;
        height: 100%;
        z-index: 100;
        box-shadow: 2px 0 8px var(--shadow);
        transform: translateX(-100%);
    }

    .sidebar:not(.collapsed) {
        transform: translateX(0);
    }

    .sidebar.collapsed {
        transform: translateX(-100%);
    }

    .login-content {
        padding: 40px 32px;
    }

    .chat-messages {
        padding: 16px;
    }

    .chat-header {
        padding: 12px 16px;
    }

    .header-title h1 {
        font-size: 1.1rem;
    }

    .message {
        gap: 8px;
    }

    .message-avatar {
        width: 32px;
        height: 32px;
        font-size: 1.1rem;
    }

    .message-content {
        padding: 10px 12px;
        font-size: 0.95rem;
    }

    .chat-input-container {
        padding: 12px;
    }
}

@media (max-width: 480px) {
    .login-content {
        padding: 32px 24px;
    }

    .login-logo {
        font-size: 3rem;
    }

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

    .chat-messages {
        padding: 12px;
        gap: 12px;
    }

    .message-content {
        font-size: 0.9rem;
    }
}