/* ===== 全局样式重置 ===== */
:root {
    --primary: #2563eb;
    --primary-hover: #1d4ed8;
    --primary-light: #dbeafe;
    --bg: #f8fafc;
    --bg-card: #ffffff;
    --text: #1e293b;
    --text-secondary: #64748b;
    --border: #e2e8f0;
    --shadow: 0 1px 3px rgba(0,0,0,0.1);
    --shadow-lg: 0 4px 12px rgba(0,0,0,0.1);
    --radius: 8px;
    --radius-lg: 12px;
    --header-height: 60px;
    --footer-bg: #1e293b;
    --footer-text: #cbd5e1;
}

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

body {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, "Noto Sans SC", sans-serif;
    background: var(--bg);
    color: var(--text);
    line-height: 1.6;
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}

a { color: var(--primary); text-decoration: none; }
a:hover { text-decoration: underline; }

/* ===== Header ===== */
header {
    background: var(--bg-card);
    border-bottom: 1px solid var(--border);
    height: var(--header-height);
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 0 24px;
    position: sticky;
    top: 0;
    z-index: 100;
    box-shadow: var(--shadow);
}

header .logo {
    font-size: 1.1rem;
    font-weight: 700;
    color: var(--primary);
    display: flex;
    align-items: center;
    gap: 8px;
}

header nav { display: flex; align-items: center; gap: 16px; }

header nav a {
    color: var(--text-secondary);
    font-size: 0.9rem;
    font-weight: 500;
    padding: 6px 12px;
    border-radius: var(--radius);
    transition: background 0.2s, color 0.2s;
}

header nav a:hover {
    background: var(--primary-light);
    color: var(--primary);
    text-decoration: none;
}

.lang-switch {
    padding: 6px 12px;
    border: 1px solid var(--border);
    border-radius: var(--radius);
    font-size: 0.85rem;
    cursor: pointer;
    background: var(--bg-card);
    color: var(--text);
    transition: border-color 0.2s;
}

.lang-switch:hover { border-color: var(--primary); }

/* ===== Hreflang 提示（不可见，仅用于SEO） ===== */
.hreflang { display: none; }

/* ===== 主内容区 ===== */
main { flex: 1; max-width: 1100px; margin: 0 auto; padding: 40px 24px; width: 100%; }

.page-header { text-align: center; margin-bottom: 40px; }

.page-header h1 {
    font-size: 1.8rem;
    font-weight: 700;
    color: var(--text);
    margin-bottom: 8px;
}

.page-header p {
    font-size: 1rem;
    color: var(--text-secondary);
    max-width: 600px;
    margin: 0 auto;
}

/* ===== 工具网格布局 ===== */
.tool-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
    gap: 20px;
    margin-bottom: 40px;
}

.tool-card {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius-lg);
    padding: 24px;
    transition: box-shadow 0.2s, transform 0.2s;
    cursor: pointer;
}

.tool-card:hover {
    box-shadow: var(--shadow-lg);
    transform: translateY(-2px);
}

.tool-card .icon {
    font-size: 2rem;
    margin-bottom: 12px;
}

.tool-card h3 {
    font-size: 1.1rem;
    font-weight: 600;
    margin-bottom: 6px;
}

.tool-card p {
    font-size: 0.9rem;
    color: var(--text-secondary);
    line-height: 1.5;
}

/* ===== 计算器表单样式 ===== */
.calculator-form {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius-lg);
    padding: 32px;
    max-width: 600px;
    margin: 0 auto 40px;
}

.calculator-form h2 {
    font-size: 1.3rem;
    margin-bottom: 24px;
    text-align: center;
}

.form-group {
    margin-bottom: 16px;
}

.form-group label {
    display: block;
    font-size: 0.9rem;
    font-weight: 500;
    margin-bottom: 4px;
    color: var(--text);
}

.form-group input,
.form-group select {
    width: 100%;
    padding: 10px 12px;
    border: 1px solid var(--border);
    border-radius: var(--radius);
    font-size: 1rem;
    transition: border-color 0.2s;
    background: var(--bg-card);
    color: var(--text);
}

.form-group input:focus,
.form-group select:focus {
    outline: none;
    border-color: var(--primary);
    box-shadow: 0 0 0 3px var(--primary-light);
}

.form-row {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 16px;
}

.btn-group {
    display: flex;
    gap: 12px;
    margin-top: 24px;
}

.btn {
    flex: 1;
    padding: 12px 24px;
    border: none;
    border-radius: var(--radius);
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    transition: background 0.2s;
}

.btn-primary {
    background: var(--primary);
    color: #fff;
}

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

.btn-secondary {
    background: var(--border);
    color: var(--text);
}

.btn-secondary:hover { background: #cbd5e1; }

/* ===== 结果卡片 ===== */
.result-card {
    background: var(--primary-light);
    border: 1px solid #bfdbfe;
    border-radius: var(--radius-lg);
    padding: 24px;
    margin-top: 24px;
    text-align: center;
}

.result-card h3 {
    font-size: 1rem;
    color: var(--text-secondary);
    margin-bottom: 8px;
}

.result-card .result-value {
    font-size: 2rem;
    font-weight: 700;
    color: var(--primary);
}

.result-card .result-detail {
    font-size: 0.9rem;
    color: var(--text-secondary);
    margin-top: 8px;
}

/* ===== 图表容器 ===== */
.chart-container {
    max-width: 600px;
    margin: 24px auto;
    padding: 16px;
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius-lg);
}

/* ===== 广告位占位 ===== */
.ad-placeholder {
    background: var(--border);
    border-radius: var(--radius);
    padding: 40px 20px;
    text-align: center;
    color: var(--text-secondary);
    font-size: 0.85rem;
    margin: 24px 0;
    min-height: 90px;
    display: flex;
    align-items: center;
    justify-content: center;
}

/* ===== 页脚 ===== */
footer {
    background: var(--footer-bg);
    color: var(--footer-text);
    text-align: center;
    padding: 32px 24px;
    font-size: 0.85rem;
    margin-top: auto;
}

footer a { color: #93c5fd; }
footer a:hover { color: #fff; }

/* ===== 响应式 ===== */
@media (max-width: 768px) {
    header { padding: 0 16px; }
    header .logo { font-size: 1rem; }
    main { padding: 24px 16px; }
    .page-header h1 { font-size: 1.4rem; }
    .tool-grid { grid-template-columns: 1fr; }
    .calculator-form { padding: 20px; }
    .form-row { grid-template-columns: 1fr; }
    .btn-group { flex-direction: column; }
    .result-card .result-value { font-size: 1.5rem; }
}

@media (max-width: 480px) {
    .page-header h1 { font-size: 1.2rem; }
    .tool-card { padding: 16px; }
    .tool-card .icon { font-size: 1.5rem; }
}
/* ===== 语言选择页 ===== */
.lang-select-page {
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    min-height: 100vh;
    text-align: center;
    padding: 20px;
}
.lang-select-page h1 {
    font-size: 2rem;
    margin-bottom: 40px;
    color: var(--text);
}
.lang-select-options {
    display: flex;
    gap: 20px;
    flex-wrap: wrap;
    justify-content: center;
}
.lang-select-card {
    display: block;
    padding: 24px 48px;
    background: var(--primary);
    color: white;
    border-radius: var(--radius-lg);
    text-decoration: none;
    font-size: 1.2rem;
    font-weight: 600;
    transition: background 0.2s, transform 0.2s;
}
.lang-select-card:hover {
    background: var(--primary-hover);
    transform: translateY(-2px);
    text-decoration: none;
    color: white;
}
/* 语言选择页结束 */
@