:root {
    --bg: #050505;
    --surface: #0c0c0c;
    --surface-hover: #141414;
    --border: #1a1a1a;
    --border-glow: #dc262620;
    --text: #d4d4d4;
    --text-dim: #555;
    --text-faint: #333;
    --accent: #dc2626;
    --accent-bright: #ff3333;
    --accent-dim: #7f1d1d;
    --accent-glow: #dc262615;
    --user-bg: #0d0d18;
    --ai-bg: #0a0a0a;
}

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

body {
    background: var(--bg);
    color: var(--text);
    font-family: 'Inter', system-ui, -apple-system, sans-serif;
    height: 100dvh;
    display: flex;
    flex-direction: column;
    overflow: hidden;
}

/* ── Header ── */
.header {
    padding: 1.25rem 1.5rem 1rem;
    text-align: center;
    flex-shrink: 0;
    position: relative;
    background: linear-gradient(180deg, #0a0000 0%, var(--bg) 100%);
}

.header::after {
    content: '';
    position: absolute;
    bottom: 0;
    left: 0;
    right: 0;
    height: 1px;
    background: linear-gradient(90deg, transparent 0%, var(--accent-dim) 50%, transparent 100%);
}

.header h1 {
    font-size: 1.5rem;
    font-weight: 800;
    letter-spacing: 0.25em;
    color: var(--accent);
    text-transform: uppercase;
    text-shadow: 0 0 40px #dc262640, 0 0 80px #dc262620;
}

.header p {
    color: #888;
    font-size: 0.75rem;
    margin-top: 0.35rem;
    letter-spacing: 0.06em;
    font-weight: 400;
}

/* ── Chat area ── */
.chat-container {
    flex: 1;
    overflow-y: auto;
    padding: 1.5rem;
    display: flex;
    flex-direction: column;
    gap: 1rem;
    scroll-behavior: smooth;
}

::-webkit-scrollbar { width: 4px; }
::-webkit-scrollbar-track { background: transparent; }
::-webkit-scrollbar-thumb { background: var(--border); border-radius: 2px; }

/* ── Messages ── */
.message {
    max-width: 780px;
    width: 100%;
    margin: 0 auto;
    padding: 1.1rem 1.4rem;
    border-radius: 10px;
    line-height: 1.65;
    font-size: 0.92rem;
    animation: fadeIn 0.25s ease;
}

@keyframes fadeIn {
    from { opacity: 0; transform: translateY(6px); }
    to { opacity: 1; transform: translateY(0); }
}

.message.user {
    background: var(--user-bg);
    border: 1px solid #1a1a30;
}

.message.assistant {
    background: var(--ai-bg);
    border: 1px solid var(--border);
    border-left: 2px solid var(--accent-dim);
}

.message .role {
    font-size: 0.6rem;
    font-weight: 700;
    text-transform: uppercase;
    letter-spacing: 0.12em;
    margin-bottom: 0.6rem;
}

.message.user .role { color: #4f46e5; }
.message.assistant .role { color: var(--accent); }

.message .content p { margin-bottom: 0.75rem; }
.message .content p:last-child { margin-bottom: 0; }
.message .content strong { color: #fff; }
.message .content em { color: var(--accent-bright); font-style: normal; font-weight: 600; }
.message .content ul, .message .content ol { margin: 0.5rem 0 0.75rem 1.25rem; }
.message .content li { margin-bottom: 0.25rem; }
.message .content code {
    background: #111;
    padding: 0.15rem 0.4rem;
    border-radius: 3px;
    font-size: 0.85em;
    color: #f87171;
    border: 1px solid #1a1a1a;
}
.message .content pre {
    background: #080808;
    padding: 0.75rem 1rem;
    border-radius: 6px;
    overflow-x: auto;
    margin: 0.5rem 0;
    border: 1px solid var(--border);
}
.message .content pre code {
    background: none;
    padding: 0;
    color: var(--text);
    border: none;
}
.message .content h1, .message .content h2, .message .content h3 {
    color: #fff;
    margin: 1rem 0 0.5rem;
}
.message .content h1 { font-size: 1.2rem; }
.message .content h2 { font-size: 1.05rem; }
.message .content h3 { font-size: 0.95rem; }

/* ── Welcome screen ── */
.welcome {
    flex: 1;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    text-align: center;
    padding: 2rem;
    gap: 1.25rem;
}

.welcome-icon {
    width: 64px;
    height: 64px;
    border-radius: 50%;
    background: radial-gradient(circle, #dc262625 0%, transparent 70%);
    border: 1px solid var(--accent-dim);
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 1.75rem;
    animation: pulse-glow 3s ease-in-out infinite;
}

@keyframes pulse-glow {
    0%, 100% { box-shadow: 0 0 20px #dc262610, 0 0 60px #dc262608; }
    50% { box-shadow: 0 0 30px #dc262625, 0 0 80px #dc262612; }
}

.welcome h2 {
    font-size: 1.75rem;
    font-weight: 800;
    color: #fff;
    letter-spacing: -0.02em;
}

.welcome h2 span {
    color: var(--accent);
}

.welcome p {
    color: var(--text-dim);
    max-width: 460px;
    line-height: 1.6;
    font-size: 0.88rem;
}

.welcome .suggestions {
    display: flex;
    flex-wrap: wrap;
    gap: 0.5rem;
    justify-content: center;
    margin-top: 0.5rem;
}

.welcome .suggestions button {
    background: transparent;
    border: 1px solid var(--border);
    color: var(--text-dim);
    padding: 0.55rem 1.1rem;
    border-radius: 6px;
    font-size: 0.8rem;
    cursor: pointer;
    transition: all 0.2s;
    font-family: inherit;
    letter-spacing: 0.01em;
}

.welcome .suggestions button:hover {
    border-color: var(--accent-dim);
    color: var(--text);
    background: var(--accent-glow);
    box-shadow: 0 0 20px #dc262610;
}

/* ── Grade badges (rendered in markdown) ── */
.message .content p em:first-child {
    display: inline-block;
    padding: 0.1rem 0.5rem;
    border-radius: 3px;
    font-size: 0.75rem;
    letter-spacing: 0.08em;
    text-transform: uppercase;
}

/* ── Input area ── */
.input-area {
    padding: 1rem 1.5rem;
    border-top: 1px solid var(--border);
    background: var(--surface);
    flex-shrink: 0;
    position: relative;
}

.input-area::before {
    content: '';
    position: absolute;
    top: -1px;
    left: 0;
    right: 0;
    height: 1px;
    background: linear-gradient(90deg, transparent 0%, #dc262630 50%, transparent 100%);
}

.input-wrap {
    max-width: 780px;
    margin: 0 auto;
    display: flex;
    gap: 0.75rem;
    align-items: flex-end;
}

.input-wrap textarea {
    flex: 1;
    background: var(--bg);
    border: 1px solid var(--border);
    border-radius: 8px;
    color: var(--text);
    padding: 0.75rem 1rem;
    font-family: inherit;
    font-size: 0.9rem;
    resize: none;
    height: 44px;
    max-height: 200px;
    line-height: 1.5;
    outline: none;
    overflow-y: hidden;
    transition: border-color 0.2s, box-shadow 0.2s;
}

.input-wrap textarea:focus {
    border-color: var(--accent-dim);
    box-shadow: 0 0 0 1px #dc262615, 0 0 20px #dc262608;
}

.input-wrap textarea::placeholder {
    color: var(--text-faint);
}

.input-wrap button {
    background: var(--accent);
    color: #fff;
    border: none;
    border-radius: 8px;
    padding: 0.75rem 1.5rem;
    font-weight: 700;
    font-size: 0.8rem;
    cursor: pointer;
    transition: all 0.15s;
    white-space: nowrap;
    height: 44px;
    letter-spacing: 0.06em;
    text-transform: uppercase;
}

.input-wrap button:hover {
    background: var(--accent-bright);
    box-shadow: 0 0 20px #dc262630;
}

.input-wrap button:disabled {
    background: var(--accent-dim);
    cursor: not-allowed;
    opacity: 0.5;
    box-shadow: none;
}

/* ── Header logo ── */
.header-logo {
    position: absolute;
    left: 1.25rem;
    top: 50%;
    transform: translateY(-50%);
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 0.1rem;
    text-decoration: none;
    opacity: 0.35;
    transition: opacity 0.2s;
}

.header-logo:hover { opacity: 0.7; }

.header-logo span {
    font-size: 0.5rem;
    color: #999;
    letter-spacing: 0.08em;
    text-transform: uppercase;
}

.header-logo img {
    height: 56px;
    width: auto;
}

/* ── Typing indicator ── */
.typing-indicator {
    display: inline-flex;
    gap: 5px;
    padding: 4px 0;
}

.typing-indicator span {
    width: 5px;
    height: 5px;
    background: var(--accent);
    border-radius: 50%;
    animation: bounce 1.2s 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: 0.4; }
    30% { transform: translateY(-5px); opacity: 1; }
}

/* ── Responsive ── */
@media (max-width: 640px) {
    .header h1 { font-size: 1.2rem; letter-spacing: 0.2em; }
    .message { padding: 0.75rem 1rem; font-size: 0.88rem; }
    .input-area { padding: 0.75rem; }
    .welcome h2 { font-size: 1.3rem; }
    .welcome-icon { width: 48px; height: 48px; font-size: 1.25rem; }
    .header-logo { left: 0.75rem; }
    .header-logo img { height: 22px; }
    .header-logo span { display: none; }
}