:root {
    --bg-primary: #0d1117;
    --bg-secondary: #161b22;
    --bg-card: #21262d;
    --border: #30363d;
    --text-primary: #e6edf3;
    --text-secondary: #8b949e;
    --accent: #58a6ff;
    --accent-hover: #79b8ff;
    --danger: #f85149;
    --danger-hover: #ff7b72;
    --success: #3fb950;
    --shadow: 0 4px 12px rgba(0,0,0,0.4);
}

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

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    background: var(--bg-primary);
    color: var(--text-primary);
    min-height: 100vh;
    line-height: 1.6;
}

.container {
    max-width: 720px;
    margin: 0 auto;
    padding: 2rem 1rem;
}

header {
    text-align: center;
    margin-bottom: 2.5rem;
}

header h1 {
    font-size: 2.5rem;
    background: linear-gradient(90deg, var(--accent), #a371f7);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    margin-bottom: 0.5rem;
}

.subtitle {
    color: var(--text-secondary);
    font-size: 1.1rem;
}

section {
    background: var(--bg-secondary);
    border: 1px solid var(--border);
    border-radius: 12px;
    padding: 1.5rem;
    margin-bottom: 1.5rem;
    box-shadow: var(--shadow);
}

section h2 {
    font-size: 1.25rem;
    margin-bottom: 1rem;
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.count {
    color: var(--text-secondary);
    font-size: 0.9rem;
    font-weight: normal;
}

.input-group {
    margin-bottom: 1rem;
}

input, textarea {
    width: 100%;
    padding: 0.75rem 1rem;
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: 8px;
    color: var(--text-primary);
    font-size: 1rem;
    transition: border-color 0.2s;
}

input:focus, textarea:focus {
    outline: none;
    border-color: var(--accent);
}

input::placeholder, textarea::placeholder {
    color: var(--text-secondary);
}

.btn-primary {
    width: 100%;
    padding: 0.75rem;
    background: var(--accent);
    color: #fff;
    border: none;
    border-radius: 8px;
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    transition: background 0.2s, transform 0.1s;
}

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

.btn-primary:active {
    transform: scale(0.98);
}

.loading {
    text-align: center;
    color: var(--text-secondary);
    padding: 2rem;
}

.topics-list {
    display: flex;
    flex-direction: column;
    gap: 0.75rem;
}

.topic-card {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: 10px;
    padding: 1rem;
    display: flex;
    justify-content: space-between;
    align-items: flex-start;
    transition: border-color 0.2s, box-shadow 0.2s;
}

.topic-card:hover {
    border-color: var(--accent);
    box-shadow: 0 0 0 1px var(--accent);
}

.topic-info {
    flex: 1;
}

.topic-title {
    font-size: 1.1rem;
    font-weight: 600;
    margin-bottom: 0.25rem;
}

.topic-desc {
    color: var(--text-secondary);
    font-size: 0.9rem;
}

.topic-meta {
    display: flex;
    align-items: center;
    gap: 0.75rem;
    margin-top: 0.5rem;
    font-size: 0.8rem;
    color: var(--text-secondary);
}

.topic-actions {
    display: flex;
    gap: 0.5rem;
}

.btn-learned {
    padding: 0.4rem 0.8rem;
    background: transparent;
    border: 1px solid var(--success);
    color: var(--success);
    border-radius: 6px;
    cursor: pointer;
    font-size: 0.85rem;
    transition: all 0.2s;
}

.btn-learned:hover {
    background: var(--success);
    color: var(--bg-primary);
}

.btn-learned.learned {
    background: var(--success);
    color: var(--bg-primary);
}

.btn-delete {
    padding: 0.4rem 0.8rem;
    background: transparent;
    border: 1px solid var(--danger);
    color: var(--danger);
    border-radius: 6px;
    cursor: pointer;
    font-size: 0.85rem;
    transition: all 0.2s;
}

.btn-delete:hover {
    background: var(--danger);
    color: #fff;
}

.empty-state {
    text-align: center;
    color: var(--text-secondary);
    padding: 3rem 1rem;
}

.empty-state-icon {
    font-size: 3rem;
    margin-bottom: 1rem;
    opacity: 0.5;
}

footer {
    text-align: center;
    color: var(--text-secondary);
    font-size: 0.85rem;
    margin-top: 2rem;
}

@media (max-width: 480px) {
    header h1 { font-size: 2rem; }
    .topic-card { flex-direction: column; gap: 0.75rem; }
    .topic-actions { align-self: flex-end; }
}