/* 黑白主色调 */
:root {
    --black: #000000;
    --white: #ffffff;
    --gray-100: #f5f5f5;
    --gray-200: #eeeeee;
    --gray-300: #e0e0e0;
    --gray-400: #bdbdbd;
    --gray-500: #9e9e9e;
    --gray-600: #757575;
    --gray-700: #616161;
    --gray-800: #424242;
    --gray-900: #212121;
}

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

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, sans-serif;
    background-color: var(--white);
    color: var(--gray-900);
    line-height: 1.6;
}

/* 导航 */
.nav {
    border-bottom: 1px solid var(--gray-200);
    padding: 1.5rem 2rem;
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.logo svg {
    height: 40px;
    width: auto;
}

.nav-links {
    display: flex;
    gap: 2rem;
}

.nav-links a {
    color: var(--gray-900);
    text-decoration: none;
    font-weight: 500;
    font-size: 0.9rem;
    letter-spacing: 0.5px;
}

.nav-links a:hover {
    text-decoration: underline;
}

/* 主体容器 */
.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 2rem;
}

/* Hero 区域 */
.hero {
    padding: 4rem 0;
    border-bottom: 1px solid var(--gray-200);
}

.hero h1 {
    font-size: 4rem;
    font-weight: 700;
    letter-spacing: -2px;
    line-height: 1.1;
    margin-bottom: 1.5rem;
}

.hero .subhead {
    font-size: 1.5rem;
    color: var(--gray-600);
    max-width: 800px;
    margin-bottom: 2rem;
}

/* 标签 */
.tag {
    display: inline-block;
    padding: 0.25rem 1rem;
    background-color: var(--gray-900);
    color: var(--white);
    font-size: 0.8rem;
    letter-spacing: 1px;
    margin-bottom: 1rem;
}

/* 本期问题卡片 */
.current-question {
    background-color: var(--gray-100);
    padding: 3rem;
    margin: 3rem 0;
    border: 1px solid var(--gray-200);
}

.question-title {
    font-size: 2rem;
    font-weight: 600;
    margin-bottom: 1rem;
}

.question-meta {
    color: var(--gray-600);
    margin-bottom: 2rem;
    font-size: 1.1rem;
}

.question-desc {
    font-size: 1.2rem;
    margin-bottom: 2rem;
    max-width: 800px;
}

/* 表单 */
.form-section {
    background-color: var(--white);
    border: 1px solid var(--gray-200);
    padding: 3rem;
    margin: 3rem 0;
}

.form-grid {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: 2rem;
}

.form-group {
    margin-bottom: 1.5rem;
}

.form-group.full-width {
    grid-column: 1 / -1;
}

label {
    display: block;
    margin-bottom: 0.5rem;
    font-weight: 500;
    font-size: 0.9rem;
    letter-spacing: 0.5px;
}

input, textarea, select {
    width: 100%;
    padding: 1rem;
    border: 1px solid var(--gray-300);
    background-color: var(--white);
    font-size: 1rem;
    transition: all 0.2s;
}

input:focus, textarea:focus, select:focus {
    outline: none;
    border-color: var(--gray-900);
    background-color: var(--white);
}

textarea {
    min-height: 150px;
    resize: vertical;
}

.hint {
    color: var(--gray-600);
    font-size: 0.9rem;
    margin-top: 0.5rem;
}

/* 按钮 */
.btn {
    display: inline-block;
    padding: 1rem 3rem;
    background-color: var(--gray-900);
    color: var(--white);
    text-decoration: none;
    border: none;
    font-size: 1rem;
    font-weight: 600;
    letter-spacing: 1px;
    cursor: pointer;
    transition: all 0.2s;
    border: 1px solid var(--gray-900);
}

.btn:hover {
    background-color: var(--white);
    color: var(--gray-900);
}

.btn-outline {
    background-color: transparent;
    color: var(--gray-900);
    border: 1px solid var(--gray-900);
}

.btn-outline:hover {
    background-color: var(--gray-900);
    color: var(--white);
}

/* 机制卡片 */
.mechanism {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 2rem;
    margin: 4rem 0;
}

.card {
    border: 1px solid var(--gray-200);
    padding: 2rem;
}

.card h3 {
    font-size: 1.5rem;
    margin-bottom: 1rem;
    font-weight: 600;
}

.card .number {
    font-size: 3rem;
    font-weight: 700;
    color: var(--gray-300);
    margin-bottom: 1rem;
}

/* 列表 */
.list-section {
    margin: 4rem 0;
}

.list-item {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 1rem 0;
    border-bottom: 1px solid var(--gray-200);
}

.list-item:last-child {
    border-bottom: none;
}

.list-item .date {
    color: var(--gray-600);
    font-size: 0.9rem;
}

/* 底部 */
.footer {
    border-top: 1px solid var(--gray-200);
    padding: 2rem;
    text-align: center;
    color: var(--gray-600);
    font-size: 0.9rem;
}

/* 响应式 */
@media (max-width: 768px) {
    .hero h1 {
        font-size: 2.5rem;
    }
    
    .form-grid {
        grid-template-columns: 1fr;
    }
    
    .mechanism {
        grid-template-columns: 1fr;
    }
    
    .current-question {
        padding: 2rem;
    }
    
    .form-section {
        padding: 2rem;
    }
}

/* 黑白切换效果 */
.toggle-mode {
    position: fixed;
    bottom: 2rem;
    right: 2rem;
    width: 48px;
    height: 48px;
    border-radius: 50%;
    background-color: var(--gray-900);
    color: var(--white);
    border: none;
    cursor: pointer;
    font-size: 1.2rem;
    z-index: 100;
}

.toggle-mode:hover {
    transform: scale(1.1);
}

/* 黑白模式切换类 */
body.dark-mode {
    background-color: var(--gray-900);
    color: var(--white);
}

.dark-mode .nav {
    border-bottom-color: var(--gray-700);
}

.dark-mode .card,
.dark-mode .current-question,
.dark-mode .form-section {
    background-color: var(--gray-800);
    border-color: var(--gray-700);
}

.dark-mode input,
.dark-mode textarea,
.dark-mode select {
    background-color: var(--gray-800);
    border-color: var(--gray-700);
    color: var(--white);
}

.dark-mode .tag {
    background-color: var(--white);
    color: var(--gray-900);
}