/* ============== CSS Variables (Claude.ai 风格明亮淡黄主题) ============== */
:root {
    --primary-color: #4a90d9;
    --primary-hover: #3a7bc8;
    --bg-main: #f7f5f0;
    --bg-sidebar: #f0ede6;
    --bg-input: #fdfbf7;
    --bg-message-user: #ffffff;
    --bg-message-assistant: #faf8f3;
    --text-primary: #1a1a1a;
    --text-secondary: #555555;
    --text-muted: #777777;
    --border-color: #e5e2db;
    --accent-green: #42b883;
    --accent-blue: #4a90d9;
    --accent-orange: #f5a623;
    --accent-purple: #9b59b6;
    --shadow: 0 4px 12px rgba(0, 0, 0, 0.08);
    --radius: 12px;
    --radius-sm: 8px;
    --transition: all 0.2s ease;
}

/* ============== Reset & Base ============== */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
    background: var(--bg-main);
    color: var(--text-primary);
    height: 100vh;
    overflow: hidden;
}

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

/* ============== Sidebar ============== */
.sidebar {
    width: 260px;
    background: var(--bg-sidebar);
    border-right: 1px solid var(--border-color);
    display: flex;
    flex-direction: column;
    transition: var(--transition);
}

.sidebar-header {
    padding: 20px;
    border-bottom: 1px solid var(--border-color);
}

.logo {
    font-size: 18px;
    font-weight: 600;
    color: var(--text-primary);
    white-space: nowrap;
}

.new-chat-btn {
    margin: 16px;
    padding: 12px 16px;
    background: var(--primary-color);
    color: white;
    border: none;
    border-radius: var(--radius-sm);
    font-size: 14px;
    cursor: pointer;
    transition: var(--transition);
    display: flex;
    align-items: center;
    gap: 8px;
}

.new-chat-btn:hover {
    background: var(--primary-hover);
}

.new-chat-btn span {
    font-size: 18px;
    font-weight: bold;
}

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

.session-item {
    padding: 12px;
    border-radius: var(--radius-sm);
    cursor: pointer;
    margin-bottom: 4px;
    transition: var(--transition);
    display: flex;
    align-items: center;
    gap: 8px;
}

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

.session-item.active {
    background: var(--primary-color);
    color: white;
}

.session-item .session-icon {
    font-size: 16px;
}

.session-item .session-preview {
    flex: 1;
    font-size: 13px;
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
}

.session-item .delete-session {
    opacity: 0;
    padding: 4px;
    background: none;
    border: none;
    color: var(--text-secondary);
    cursor: pointer;
    transition: var(--transition);
}

.session-item:hover .delete-session {
    opacity: 1;
}

.session-item .delete-session:hover {
    color: #e53935;
}

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

.chat-header {
    padding: 16px 24px;
    border-bottom: 1px solid var(--border-color);
    display: flex;
    align-items: center;
    gap: 16px;
    background: var(--bg-main);
}

.menu-toggle {
    display: none;
    background: none;
    border: none;
    color: var(--text-primary);
    font-size: 20px;
    cursor: pointer;
    padding: 4px;
}

.menu-toggle:hover {
    color: var(--primary-color);
}

.chat-header h2 {
    flex: 1;
    font-size: 16px;
    font-weight: 500;
}

.header-actions {
    display: flex;
    gap: 8px;
}

.icon-btn {
    background: none;
    border: none;
    color: var(--text-secondary);
    font-size: 18px;
    cursor: pointer;
    padding: 8px;
    border-radius: var(--radius-sm);
    transition: var(--transition);
}

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

/* ============== Model Selector (Beautiful Select) ============== */
.model-select {
    appearance: none;
    -webkit-appearance: none;
    -moz-appearance: none;
    padding: 8px 36px 8px 14px;
    background: var(--bg-input);
    border: 1.5px solid var(--border-color);
    border-radius: 20px;
    font-size: 13px;
    font-weight: 500;
    color: var(--text-primary);
    cursor: pointer;
    outline: none;
    transition: all 0.25s ease;
    background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='12' height='12' viewBox='0 0 12 12'%3E%3Cpath fill='%23555' d='M6 8L1 3h10z'/%3E%3C/svg%3E");
    background-repeat: no-repeat;
    background-position: right 12px center;
}

.model-select:hover {
    border-color: var(--primary-color);
    box-shadow: 0 2px 8px rgba(74, 144, 217, 0.15);
}

.model-select:focus {
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px rgba(74, 144, 217, 0.2), 0 2px 8px rgba(74, 144, 217, 0.15);
}

.model-select option {
    padding: 10px;
    background: var(--bg-input);
    color: var(--text-primary);
    border-radius: 8px;
}

/* ============== Messages Container ============== */
.messages-container {
    flex: 1;
    overflow-y: auto;
    padding: 24px;
    display: flex;
    flex-direction: column;
}

/* Welcome Message */
.welcome-message {
    text-align: center;
    padding: 60px 20px;
    max-width: 600px;
    margin: 0 auto;
}

.welcome-icon {
    font-size: 48px;
    margin-bottom: 20px;
}

.welcome-message h2 {
    font-size: 24px;
    margin-bottom: 12px;
    color: var(--text-primary);
}

.welcome-message p {
    color: var(--text-secondary);
    margin-bottom: 32px;
}

.feature-list {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: 16px;
    margin-bottom: 32px;
}

.feature-item {
    display: flex;
    align-items: center;
    gap: 12px;
    padding: 12px 16px;
    background: var(--bg-input);
    border-radius: var(--radius-sm);
}

.feature-icon {
    font-size: 20px;
}

.quick-terms p {
    color: var(--text-muted);
    margin-bottom: 12px;
}

.quick-term-btns {
    display: flex;
    flex-wrap: wrap;
    gap: 8px;
    justify-content: center;
}

.quick-term-btn {
    padding: 8px 16px;
    background: var(--bg-input);
    border: 1px solid var(--border-color);
    color: var(--text-primary);
    border-radius: 20px;
    font-size: 13px;
    cursor: pointer;
    transition: var(--transition);
}

.quick-term-btn:hover {
    background: var(--primary-color);
    border-color: var(--primary-color);
}

/* Messages List */
.messages-list {
    display: flex;
    flex-direction: column;
    gap: 20px;
}

.message {
    display: flex;
    gap: 12px;
    max-width: 85%;
    animation: fadeIn 0.3s ease;
}

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

.message.user {
    align-self: flex-end;
    flex-direction: row-reverse;
}

.message-avatar {
    width: 32px;
    height: 32px;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 16px;
    flex-shrink: 0;
}

.message.user .message-avatar {
    background: var(--accent-blue);
}

.message.assistant .message-avatar {
    background: var(--accent-green);
}

.message-content {
    padding: 14px 18px;
    border-radius: var(--radius);
    background: var(--bg-message-user);
}

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

.message.assistant .message-content {
    background: var(--bg-message-assistant);
}

.message.assistant .message-content .markdown-body {
    color: var(--text-primary);
}

.message.assistant .message-content .markdown-body code {
    background: rgba(0, 0, 0, 0.06);
    color: var(--text-primary);
    padding: 2px 6px;
    border-radius: 4px;
    font-size: 0.9em;
}

.message.assistant .message-content .markdown-body pre {
    background: rgba(0, 0, 0, 0.05);
    padding: 12px;
    border-radius: 8px;
    overflow-x: auto;
    margin: 8px 0;
    border: 1px solid var(--border-color);
}

/* Markdown tables - light theme */
.message.assistant .message-content .markdown-body table {
    border-collapse: collapse;
    width: 100%;
    margin: 12px 0;
    font-size: 14px;
}

.message.assistant .message-content .markdown-body th {
    background: rgba(74, 144, 217, 0.12);
    color: var(--text-primary);
    font-weight: 600;
    border: 1px solid var(--border-color);
    padding: 10px 14px;
}

.message.assistant .message-content .markdown-body td {
    background: rgba(255, 255, 255, 0.6);
    color: var(--text-primary);
    border: 1px solid var(--border-color);
    padding: 8px 14px;
}

.message.assistant .message-content .markdown-body tr:nth-child(even) td {
    background: rgba(0, 0, 0, 0.02);
}

/* Markdown links - light theme */
.message.assistant .message-content .markdown-body a {
    color: #0969da;
    text-decoration: none;
}

.message.assistant .message-content .markdown-body a:hover {
    text-decoration: underline;
    color: #0550ae;
}

.message.assistant .message-content .markdown-body img {
    max-width: 100%;
    height: auto;
    border-radius: var(--radius);
    margin: 8px 0;
}

/* ============== Input Area ============== */
.input-container {
    padding: 16px 24px 24px;
    background: var(--bg-main);
}

.input-wrapper {
    display: flex;
    align-items: flex-end;
    gap: 12px;
    background: var(--bg-input);
    border: 1px solid var(--border-color);
    border-radius: var(--radius);
    padding: 12px 16px;
    transition: var(--transition);
}

.input-wrapper:focus-within {
    border-color: var(--primary-color);
    box-shadow: 0 0 0 2px rgba(74, 144, 217, 0.2);
}

#messageInput {
    flex: 1;
    background: transparent;
    border: none;
    color: var(--text-primary);
    font-size: 15px;
    resize: none;
    outline: none;
    max-height: 150px;
    line-height: 1.5;
}

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

.send-btn {
    background: var(--primary-color);
    border: none;
    color: white;
    width: 36px;
    height: 36px;
    border-radius: var(--radius-sm);
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: var(--transition);
    flex-shrink: 0;
}

.send-btn:hover {
    background: var(--primary-hover);
}

.send-btn:disabled {
    background: var(--text-muted);
    cursor: not-allowed;
}

.input-hint {
    margin-top: 8px;
    font-size: 12px;
    color: var(--text-muted);
    text-align: center;
}

.input-hint kbd {
    background: var(--bg-input);
    padding: 2px 6px;
    border-radius: 4px;
    font-family: inherit;
    font-size: 11px;
}

/* ============== Loading Indicator ============== */
.loading-indicator {
    position: fixed;
    bottom: 100px;
    left: 50%;
    transform: translateX(-50%);
    display: flex;
    align-items: center;
    gap: 12px;
    padding: 12px 20px;
    background: var(--bg-input);
    border-radius: 20px;
    box-shadow: var(--shadow);
    z-index: 100;
}

.typing-indicator {
    display: flex;
    gap: 4px;
}

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

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

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

@keyframes typing {
    0%, 60%, 100% { transform: translateY(0); opacity: 0.5; }
    30% { transform: translateY(-4px); opacity: 1; }
}

.loading-text {
    font-size: 13px;
    color: var(--text-secondary);
}

/* ============== Scrollbar ============== */
::-webkit-scrollbar {
    width: 8px;
    height: 8px;
}

::-webkit-scrollbar-track {
    background: transparent;
}

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

::-webkit-scrollbar-thumb:hover {
    background: var(--text-muted);
}

/* ============== Responsive ============== */
@media (max-width: 768px) {
    .sidebar {
        position: fixed;
        left: -260px;
        top: 0;
        bottom: 0;
        z-index: 1000;
    }

    .sidebar.open {
        left: 0;
    }

    .menu-toggle {
        display: block;
    }

    .message {
        max-width: 95%;
    }

    .feature-list {
        grid-template-columns: 1fr;
    }
}