/* ========== Reset & Base ========== */
*, *::before, *::after {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

:root {
    --bg: #fafaf7;
    --surface: #ffffff;
    --accent: #2d6a4f;
    --accent-light: #d8f3dc;
    --text: #1a1a1a;
    --text-muted: #6b7280;
    --border: #e5e7eb;
    --max-width: 900px;
}

body {
    font-family: 'DM Sans', -apple-system, sans-serif;
    background: var(--bg);
    color: var(--text);
    line-height: 1.7;
    font-size: 16px;
}

.container {
    max-width: var(--max-width);
    margin: 0 auto;
    padding: 0 24px;
}

a {
    color: var(--accent);
    text-decoration: none;
}

a:hover {
    text-decoration: underline;
}

/* ========== Navigation ========== */
.nav {
    border-bottom: 1px solid var(--border);
    background: var(--surface);
    position: sticky;
    top: 0;
    z-index: 100;
}

.nav-inner {
    display: flex;
    justify-content: space-between;
    align-items: center;
    height: 60px;
}

.logo {
    font-weight: 700;
    font-size: 1.1rem;
    color: var(--text);
    letter-spacing: -0.02em;
}

.logo:hover {
    text-decoration: none;
}

.nav-links {
    display: flex;
    gap: 24px;
}

.nav-links a {
    color: var(--text-muted);
    font-size: 0.9rem;
    font-weight: 500;
}

.nav-links a:hover {
    color: var(--accent);
    text-decoration: none;
}

/* ========== Hero ========== */
.hero {
    padding: 80px 0 60px;
    text-align: center;
}

.hero-tag {
    font-family: 'DM Mono', monospace;
    font-size: 0.8rem;
    color: var(--accent);
    text-transform: uppercase;
    letter-spacing: 0.1em;
    margin-bottom: 16px;
}

.hero h1 {
    font-size: clamp(2rem, 5vw, 3rem);
    font-weight: 700;
    line-height: 1.15;
    letter-spacing: -0.03em;
    margin-bottom: 20px;
}

.hero-desc {
    font-size: 1.1rem;
    color: var(--text-muted);
    max-width: 600px;
    margin: 0 auto 32px;
}

.hero-actions {
    display: flex;
    gap: 12px;
    justify-content: center;
    flex-wrap: wrap;
}

/* ========== Buttons ========== */
.btn {
    display: inline-block;
    padding: 12px 28px;
    border-radius: 6px;
    font-weight: 600;
    font-size: 0.95rem;
    transition: all 0.2s ease;
}

.btn:hover {
    text-decoration: none;
}

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

.btn-primary:hover {
    background: #1b4332;
}

.btn-secondary {
    background: var(--accent-light);
    color: var(--accent);
}

.btn-secondary:hover {
    background: #b7e4c7;
}

/* ========== Features ========== */
.features {
    padding: 40px 0 60px;
}

.features-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
    gap: 24px;
}

.feature-card {
    background: var(--surface);
    border: 1px solid var(--border);
    border-radius: 8px;
    padding: 28px;
}

.feature-icon {
    font-size: 1.5rem;
    display: block;
    margin-bottom: 12px;
}

.feature-card h3 {
    font-size: 1.1rem;
    margin-bottom: 8px;
}

.feature-card p {
    color: var(--text-muted);
    font-size: 0.9rem;
}

/* ========== Articles ========== */
.latest {
    padding: 40px 0 60px;
    border-top: 1px solid var(--border);
}

.latest h2 {
    font-size: 1.5rem;
    margin-bottom: 24px;
}

.articles-grid {
    display: grid;
    gap: 20px;
}

.article-card {
    display: block;
    background: var(--surface);
    border: 1px solid var(--border);
    border-radius: 8px;
    padding: 24px;
    color: var(--text);
    transition: border-color 0.2s ease;
}

.article-card:hover {
    border-color: var(--accent);
    text-decoration: none;
}

.article-category {
    font-family: 'DM Mono', monospace;
    font-size: 0.75rem;
    color: var(--accent);
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

.article-card h3 {
    font-size: 1.1rem;
    margin: 8px 0;
}

.article-card p {
    color: var(--text-muted);
    font-size: 0.9rem;
}

/* ========== Article Page ========== */
.article-page {
    padding: 48px 0 80px;
    max-width: 720px;
    margin: 0 auto;
    padding-left: 24px;
    padding-right: 24px;
}

.article-page .article-meta {
    font-family: 'DM Mono', monospace;
    font-size: 0.8rem;
    color: var(--text-muted);
    margin-bottom: 12px;
}

.article-page h1 {
    font-size: clamp(1.5rem, 4vw, 2.2rem);
    line-height: 1.2;
    letter-spacing: -0.02em;
    margin-bottom: 24px;
}

.article-page h2 {
    font-size: 1.3rem;
    margin-top: 40px;
    margin-bottom: 12px;
}

.article-page h3 {
    font-size: 1.1rem;
    margin-top: 28px;
    margin-bottom: 8px;
}

.article-page p {
    margin-bottom: 16px;
}

.article-page ul, .article-page ol {
    margin-bottom: 16px;
    padding-left: 24px;
}

.article-page li {
    margin-bottom: 6px;
}

.article-page table {
    width: 100%;
    border-collapse: collapse;
    margin: 20px 0;
    font-size: 0.9rem;
}

.article-page th, .article-page td {
    border: 1px solid var(--border);
    padding: 10px 14px;
    text-align: left;
}

.article-page th {
    background: var(--accent-light);
    font-weight: 600;
}

.article-page blockquote {
    border-left: 3px solid var(--accent);
    padding: 12px 20px;
    margin: 20px 0;
    background: var(--accent-light);
    border-radius: 0 6px 6px 0;
}

.article-page code {
    font-family: 'DM Mono', monospace;
    background: #f3f4f6;
    padding: 2px 6px;
    border-radius: 3px;
    font-size: 0.9em;
}

.article-page .faq {
    margin-top: 40px;
    border-top: 1px solid var(--border);
    padding-top: 24px;
}

.article-page .faq-item {
    margin-bottom: 20px;
}

.article-page .faq-item h3 {
    margin-top: 0;
    font-size: 1rem;
}

.article-page .source-note {
    margin-top: 40px;
    padding-top: 20px;
    border-top: 1px solid var(--border);
    font-size: 0.85rem;
    color: var(--text-muted);
}

/* ========== Calculator ========== */
.calculator-page {
    padding: 48px 0 80px;
    max-width: 720px;
    margin: 0 auto;
    padding-left: 24px;
    padding-right: 24px;
}

.calculator-page h1 {
    font-size: clamp(1.5rem, 4vw, 2rem);
    margin-bottom: 8px;
}

.calculator-page .subtitle {
    color: var(--text-muted);
    margin-bottom: 32px;
}

.calc-section {
    background: var(--surface);
    border: 1px solid var(--border);
    border-radius: 8px;
    padding: 24px;
    margin-bottom: 20px;
}

.calc-section h2 {
    font-size: 1.1rem;
    margin-bottom: 16px;
    display: flex;
    align-items: center;
    gap: 8px;
}

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

.form-group label {
    display: block;
    font-size: 0.9rem;
    font-weight: 500;
    margin-bottom: 6px;
}

.form-group input,
.form-group select {
    width: 100%;
    padding: 10px 14px;
    border: 1px solid var(--border);
    border-radius: 6px;
    font-size: 0.95rem;
    font-family: inherit;
    background: var(--bg);
}

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

.form-group .hint {
    font-size: 0.8rem;
    color: var(--text-muted);
    margin-top: 4px;
}

.calc-btn {
    width: 100%;
    padding: 14px;
    background: var(--accent);
    color: white;
    border: none;
    border-radius: 6px;
    font-size: 1rem;
    font-weight: 600;
    font-family: inherit;
    cursor: pointer;
    margin-top: 8px;
    transition: background 0.2s ease;
}

.calc-btn:hover {
    background: #1b4332;
}

/* Results */
.results {
    display: none;
    margin-top: 32px;
}

.results.show {
    display: block;
}

.results-box {
    background: var(--surface);
    border: 2px solid var(--accent);
    border-radius: 8px;
    padding: 32px;
    text-align: center;
}

.results-number {
    font-size: 3rem;
    font-weight: 700;
    color: var(--accent);
    line-height: 1;
}

.results-unit {
    font-size: 1rem;
    color: var(--text-muted);
    margin-bottom: 16px;
}

.results-comparison {
    font-size: 0.9rem;
    color: var(--text-muted);
    margin-top: 12px;
}

.results-breakdown {
    margin-top: 24px;
    text-align: left;
}

.results-breakdown h3 {
    font-size: 1rem;
    margin-bottom: 12px;
}

.breakdown-item {
    display: flex;
    justify-content: space-between;
    padding: 8px 0;
    border-bottom: 1px solid var(--border);
    font-size: 0.9rem;
}

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

/* ========== About Page ========== */
.about-page {
    padding: 48px 0 80px;
    max-width: 720px;
    margin: 0 auto;
    padding-left: 24px;
    padding-right: 24px;
}

.about-page h1 {
    font-size: 2rem;
    margin-bottom: 24px;
}

.about-page h2 {
    font-size: 1.3rem;
    margin-top: 32px;
    margin-bottom: 12px;
}

.about-page p {
    margin-bottom: 16px;
}

/* ========== Footer ========== */
.footer {
    border-top: 1px solid var(--border);
    padding: 24px 0;
    margin-top: 40px;
}

.footer-inner {
    display: flex;
    justify-content: space-between;
    align-items: center;
    flex-wrap: wrap;
    gap: 12px;
    font-size: 0.85rem;
    color: var(--text-muted);
}

.footer-links {
    display: flex;
    gap: 16px;
}

.footer-links a {
    color: var(--text-muted);
}

/* ========== Responsive ========== */
@media (max-width: 640px) {
    .nav-inner {
        flex-direction: column;
        height: auto;
        padding: 12px 0;
        gap: 8px;
    }

    .hero {
        padding: 48px 0 40px;
    }

    .hero-actions {
        flex-direction: column;
        align-items: center;
    }

    .footer-inner {
        flex-direction: column;
        text-align: center;
    }
}

/* ========== Social Sharing ========== */
.social-share {
    display: flex;
    gap: 12px;
    margin: 20px 0;
    padding: 16px;
    background: var(--accent-light);
    border-radius: 8px;
    justify-content: center;
    flex-wrap: wrap;
}

.social-share button {
    background: var(--surface);
    border: 1px solid var(--border);
    padding: 8px 16px;
    border-radius: 6px;
    font-size: 0.9rem;
    cursor: pointer;
    display: flex;
    align-items: center;
    gap: 6px;
    transition: all 0.2s ease;
}

.social-share button:hover {
    border-color: var(--accent);
    background: var(--accent);
    color: white;
}

.social-share button svg {
    width: 16px;
    height: 16px;
}

/* ========== Article Navigation ========== */
.article-nav {
    display: flex;
    justify-content: space-between;
    margin-top: 40px;
    padding-top: 20px;
    border-top: 1px solid var(--border);
    font-size: 0.9rem;
    gap: 16px;
}

.article-nav a {
    color: var(--accent);
}

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

/* ========== Articles List Description ========== */
.articles-desc {
    color: var(--text-muted);
    margin-bottom: 32px;
}