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

:root {
    --bg: #f7f7f8;
    --surface: #ffffff;
    --border: #e5e5e5;
    --text: #1a1a1a;
    --text-muted: #6b7280;
    --accent: #4f2d7f;
    --accent-light: #f3eef8;
    --user-bg: #4f2d7f;
    --user-text: #ffffff;
    --assistant-bg: #ffffff;
    --code-bg: #f4f4f5;
    --code-border: #e4e4e7;
    --font-sans: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
    --font-mono: "SF Mono", "Fira Code", "Fira Mono", Menlo, monospace;
}

html, body {
    height: 100%;
    font-family: var(--font-sans);
    background: var(--bg);
    color: var(--text);
}

.chat-container {
    display: flex;
    flex-direction: column;
    height: 100vh;
    max-width: 800px;
    margin: 0 auto;
    background: var(--surface);
    border-left: 1px solid var(--border);
    border-right: 1px solid var(--border);
}

/* Header */
.chat-header {
    padding: 16px 20px;
    border-bottom: 1px solid var(--border);
    background: var(--surface);
    flex-shrink: 0;
}

.header-row {
    display: flex;
    justify-content: space-between;
    align-items: flex-start;
}

.start-over-btn {
    padding: 5px 12px;
    font-size: 12px;
    font-family: var(--font-sans);
    background: var(--bg);
    border: 1px solid var(--border);
    border-radius: 6px;
    color: var(--text-muted);
    cursor: pointer;
    transition: all 0.15s;
    white-space: nowrap;
}

.start-over-btn:hover {
    color: var(--text);
    border-color: var(--text-muted);
}

.chat-header h1 {
    font-size: 18px;
    font-weight: 600;
    color: var(--accent);
}

.chat-header .subtitle {
    font-size: 13px;
    color: var(--text-muted);
    margin-top: 2px;
}

#lesson-select {
    margin-top: 10px;
    padding: 6px 10px;
    border: 1px solid var(--border);
    border-radius: 6px;
    font-size: 13px;
    font-family: var(--font-sans);
    background: var(--bg);
    color: var(--text);
    cursor: pointer;
    width: 100%;
}

/* Messages area */
.messages {
    flex: 1;
    overflow-y: auto;
    padding: 20px;
    display: flex;
    flex-direction: column;
    gap: 16px;
}

.message {
    display: flex;
    max-width: 85%;
    animation: fadeIn 0.2s ease-in;
}

@keyframes fadeIn {
    from { opacity: 0; transform: translateY(4px); }
    to { opacity: 1; transform: translateY(0); }
}

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

.message.assistant {
    align-self: flex-start;
}

.message-content {
    padding: 10px 14px;
    border-radius: 12px;
    font-size: 14px;
    line-height: 1.6;
    word-wrap: break-word;
    overflow-wrap: break-word;
}

.message.user .message-content {
    background: var(--user-bg);
    color: var(--user-text);
    border-bottom-right-radius: 4px;
}

.message.assistant .message-content {
    background: var(--assistant-bg);
    color: var(--text);
    border: 1px solid var(--border);
    border-bottom-left-radius: 4px;
}

.message-content p {
    margin-bottom: 8px;
}

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

/* Lists inside messages */
.message-content ul,
.message-content ol {
    margin: 6px 0 8px 0;
    padding-left: 20px;
}

.message-content li {
    margin-bottom: 4px;
}

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

/* Headings inside messages */
.message-content h2,
.message-content h3,
.message-content h4 {
    font-size: 14px;
    font-weight: 600;
    margin: 10px 0 4px 0;
    color: var(--accent);
}

.message-content h2:first-child,
.message-content h3:first-child,
.message-content h4:first-child {
    margin-top: 0;
}

/* Code blocks inside messages */
.message-content .code-block {
    position: relative;
    margin: 8px 0;
}

.message-content .code-block .code-lang {
    position: absolute;
    top: 6px;
    left: 10px;
    font-size: 11px;
    color: var(--text-muted);
    font-family: var(--font-mono);
    text-transform: uppercase;
    letter-spacing: 0.5px;
}

.message-content .code-block .copy-btn {
    position: absolute;
    top: 6px;
    right: 6px;
    padding: 2px 8px;
    font-size: 11px;
    font-family: var(--font-sans);
    background: var(--surface);
    border: 1px solid var(--code-border);
    border-radius: 4px;
    color: var(--text-muted);
    cursor: pointer;
    opacity: 0;
    transition: opacity 0.15s;
}

.message-content .code-block:hover .copy-btn {
    opacity: 1;
}

.message-content .code-block .copy-btn:hover {
    color: var(--text);
    border-color: var(--text-muted);
}

.message-content pre {
    background: var(--code-bg);
    border: 1px solid var(--code-border);
    border-radius: 6px;
    padding: 12px;
    padding-top: 28px;
    margin: 0;
    overflow-x: auto;
    font-size: 13px;
    line-height: 1.5;
}

.message-content code {
    font-family: var(--font-mono);
    font-size: 13px;
}

.message-content :not(pre) > code {
    background: var(--code-bg);
    padding: 2px 5px;
    border-radius: 3px;
    font-size: 12px;
}

/* Callout boxes */
.message-content .callout {
    border-left: 3px solid var(--accent);
    background: var(--accent-light);
    padding: 8px 12px;
    margin: 8px 0;
    border-radius: 0 6px 6px 0;
    font-size: 13px;
    line-height: 1.5;
}

.message-content .callout-check {
    border-left-color: #16a34a;
    background: #f0fdf4;
}

.message-content .callout-tip {
    border-left-color: #d97706;
    background: #fffbeb;
}

/* Blockquotes */
.message-content blockquote {
    border-left: 3px solid var(--border);
    padding: 6px 12px;
    margin: 8px 0;
    color: var(--text-muted);
    font-style: italic;
}

/* Loading indicator */
.typing-indicator {
    display: flex;
    gap: 4px;
    padding: 12px 16px;
}

.typing-indicator span {
    width: 8px;
    height: 8px;
    background: var(--text-muted);
    border-radius: 50%;
    animation: bounce 1.4s ease-in-out 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); }
    30% { transform: translateY(-6px); }
}

/* Input area */
.chat-input {
    display: flex;
    gap: 8px;
    padding: 16px 20px;
    border-top: 1px solid var(--border);
    background: var(--surface);
    flex-shrink: 0;
    align-items: flex-end;
}

#user-input {
    flex: 1;
    padding: 10px 14px;
    border: 1px solid var(--border);
    border-radius: 12px;
    font-size: 14px;
    font-family: var(--font-sans);
    line-height: 1.5;
    resize: none;
    max-height: 150px;
    outline: none;
    transition: border-color 0.15s;
}

#user-input:focus {
    border-color: var(--accent);
}

#send-btn {
    width: 40px;
    height: 40px;
    border: none;
    border-radius: 10px;
    background: var(--accent);
    color: white;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    flex-shrink: 0;
    transition: opacity 0.15s;
}

#send-btn:hover {
    opacity: 0.9;
}

#send-btn:disabled {
    opacity: 0.4;
    cursor: not-allowed;
}

/* Error messages */
.message.error .message-content {
    background: #fef2f2;
    border-color: #fecaca;
    color: #991b1b;
}

/* Mobile adjustments */
@media (max-width: 600px) {
    .chat-container {
        border: none;
    }

    .message {
        max-width: 92%;
    }

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

    .messages {
        padding: 12px;
    }

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