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

:root {
  --bg-primary: #f8f9fa;
  --bg-white: #ffffff;
  --bg-input: #f1f3f5;
  --text-primary: #1f2937;
  --text-secondary: #4b5563;
  --text-muted: #9ca3af;
  --accent: #0891b2;
  --accent-hover: #0e7490;
  --accent-light: #ecfeff;
  --accent-green: #10b981;
  --accent-green-light: #ecfdf5;
  --border-color: #e5e7eb;
  --shadow-sm: 0 1px 3px rgba(0, 0, 0, 0.06);
  --shadow: 0 4px 16px rgba(0, 0, 0, 0.08);
  --shadow-lg: 0 8px 32px rgba(0, 0, 0, 0.1);
  --radius: 16px;
  --radius-sm: 10px;
  --transition: 0.2s ease;
}

html {
  font-size: 16px;
  scroll-behavior: smooth;
}

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

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

a:hover {
  color: var(--accent-hover);
}

/* ===== Header / Nav ===== */
.site-header {
  background: var(--bg-white);
  box-shadow: 0 1px 0 var(--border-color);
  position: sticky;
  top: 0;
  z-index: 100;
}

.nav-container {
  max-width: 1100px;
  margin: 0 auto;
  padding: 0 1.5rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 64px;
}

.nav-logo {
  font-size: 1.25rem;
  font-weight: 700;
  color: var(--text-primary);
  display: flex;
  align-items: center;
  gap: 0.4rem;
}

.nav-logo .logo-icon {
  display: none;
}

.nav-logo img {
  width: 36px;
  height: 36px;
  border-radius: 8px;
  object-fit: cover;
}

.nav-links {
  list-style: none;
  display: flex;
  gap: 2rem;
}

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

.nav-links a:hover,
.nav-links a.active {
  color: var(--accent);
}

.nav-toggle {
  display: none;
  background: none;
  border: none;
  color: var(--text-primary);
  font-size: 1.5rem;
  cursor: pointer;
}

/* ===== Main Content ===== */
main {
  flex: 1;
  max-width: 1100px;
  margin: 0 auto;
  padding: 2.5rem 1.5rem;
  width: 100%;
}

/* ===== Calculator Section ===== */
.calculator-hero {
  text-align: center;
  margin-bottom: 2.5rem;
}

.calculator-hero h1 {
  font-size: 2.25rem;
  font-weight: 800;
  color: var(--text-primary);
  margin-bottom: 0.5rem;
}

.calculator-hero p {
  color: var(--text-secondary);
  font-size: 1.05rem;
}

.calculator-card {
  background: var(--bg-white);
  border: 1px solid var(--border-color);
  border-radius: var(--radius);
  padding: 2rem;
  box-shadow: var(--shadow);
  max-width: 600px;
  margin: 0 auto 2rem;
}

.form-group {
  margin-bottom: 1.25rem;
}

.form-group label {
  display: block;
  font-size: 0.85rem;
  font-weight: 600;
  color: var(--text-secondary);
  margin-bottom: 0.4rem;
  letter-spacing: 0.3px;
}

.form-group input {
  width: 100%;
  padding: 0.75rem 1rem;
  background: var(--bg-input);
  border: 1.5px solid var(--border-color);
  border-radius: var(--radius-sm);
  color: var(--text-primary);
  font-size: 1.1rem;
  transition: border-color var(--transition), box-shadow var(--transition);
  outline: none;
}

.form-group input:focus {
  border-color: var(--accent);
  box-shadow: 0 0 0 3px rgba(8, 145, 178, 0.12);
  background: var(--bg-white);
}

.form-group input::placeholder {
  color: var(--text-muted);
}

.input-hint {
  font-size: 0.78rem;
  color: var(--text-muted);
  margin-top: 0.3rem;
}

/* ===== Results ===== */
.results-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 1rem;
  max-width: 600px;
  margin: 0 auto;
}

.result-card {
  background: var(--bg-white);
  border: 1px solid var(--border-color);
  border-radius: var(--radius);
  padding: 1.5rem 1rem;
  text-align: center;
  box-shadow: var(--shadow-sm);
  transition: transform var(--transition), box-shadow var(--transition);
}

.result-card:hover {
  transform: translateY(-3px);
  box-shadow: var(--shadow);
}

.result-label {
  font-size: 0.78rem;
  color: var(--text-muted);
  font-weight: 600;
  letter-spacing: 0.3px;
  margin-bottom: 0.4rem;
}

.result-value {
  font-size: 1.75rem;
  font-weight: 800;
  color: var(--accent);
  font-variant-numeric: tabular-nums;
  transition: color var(--transition);
}

.result-card:nth-child(2) .result-value {
  color: var(--accent-green);
}

.result-unit {
  font-size: 0.8rem;
  color: var(--text-muted);
  margin-top: 0.2rem;
}

/* ===== FAQ Section ===== */
.faq-section {
  max-width: 600px;
  margin: 3rem auto 0;
}

.faq-section h2 {
  font-size: 1.5rem;
  font-weight: 700;
  text-align: center;
  margin-bottom: 1.5rem;
  color: var(--text-primary);
}

.faq-item {
  background: var(--bg-white);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-sm);
  margin-bottom: 0.75rem;
  overflow: hidden;
}

.faq-question {
  width: 100%;
  padding: 1rem 1.25rem;
  background: none;
  border: none;
  text-align: left;
  font-size: 1rem;
  font-weight: 600;
  color: var(--text-primary);
  cursor: pointer;
  display: flex;
  justify-content: space-between;
  align-items: center;
  font-family: inherit;
  transition: background var(--transition);
}

.faq-question:hover {
  background: var(--bg-primary);
}

.faq-question::after {
  content: "+";
  font-size: 1.25rem;
  color: var(--accent);
  font-weight: 400;
  transition: transform var(--transition);
}

.faq-item.open .faq-question::after {
  content: "\2212";
}

.faq-answer {
  max-height: 0;
  overflow: hidden;
  transition: max-height 0.3s ease;
}

.faq-answer-inner {
  padding: 0 1.25rem 1rem;
  color: var(--text-secondary);
  line-height: 1.7;
  font-size: 0.95rem;
}

.faq-item.open .faq-answer {
  max-height: 500px;
}

/* ===== Articles List ===== */
.articles-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
  gap: 1.5rem;
  margin-top: 1.5rem;
}

.article-card {
  background: var(--bg-white);
  border: 1px solid var(--border-color);
  border-radius: var(--radius);
  padding: 1.5rem;
  box-shadow: var(--shadow-sm);
  transition: transform var(--transition), box-shadow var(--transition);
  display: flex;
  flex-direction: column;
  position: relative;
  cursor: pointer;
}

.article-card:hover {
  transform: translateY(-3px);
  box-shadow: var(--shadow);
}

.article-card h3 {
  font-size: 1.1rem;
  margin-bottom: 0.5rem;
  color: var(--text-primary);
}

.article-card h3 a {
  color: inherit;
}

.article-card h3 a::after {
  content: "";
  position: absolute;
  inset: 0;
}

.article-card h3 a:hover {
  color: var(--accent);
}

.article-card p {
  color: var(--text-secondary);
  font-size: 0.9rem;
  flex: 1;
}

.article-tag {
  display: inline-block;
  background: var(--accent-light);
  color: var(--accent);
  font-size: 0.75rem;
  font-weight: 600;
  padding: 0.2rem 0.6rem;
  border-radius: 4px;
  margin-top: 0.75rem;
  width: fit-content;
}

/* ===== Feedback Button & Modal ===== */
.feedback-wrapper {
  text-align: center;
  margin: 2rem auto;
  max-width: 600px;
}

.feedback-btn {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  padding: 0.6rem 1.5rem;
  background: var(--bg-white);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-sm);
  color: var(--text-secondary);
  font-size: 0.9rem;
  cursor: pointer;
  transition: border-color var(--transition), color var(--transition);
  font-family: inherit;
}

.feedback-btn:hover {
  border-color: var(--accent);
  color: var(--accent);
}

.feedback-overlay {
  position: fixed;
  inset: 0;
  background: rgba(0, 0, 0, 0.4);
  z-index: 200;
  display: flex;
  align-items: center;
  justify-content: center;
  visibility: hidden;
  opacity: 0;
  transition: opacity 0.2s ease, visibility 0.2s ease;
}

.feedback-overlay.open {
  visibility: visible;
  opacity: 1;
}

.feedback-modal {
  background: var(--bg-white);
  border-radius: var(--radius);
  padding: 2rem;
  width: 90%;
  max-width: 400px;
  box-shadow: var(--shadow-lg);
}

.feedback-modal h3 {
  font-size: 1.1rem;
  margin-bottom: 1rem;
  text-align: center;
}

.feedback-stars {
  display: flex;
  justify-content: center;
  gap: 0.5rem;
  margin-bottom: 1rem;
}

.feedback-stars button {
  background: none;
  border: none;
  font-size: 2rem;
  cursor: pointer;
  color: var(--border-color);
  transition: color var(--transition), transform var(--transition);
  line-height: 1;
}

.feedback-stars button.active,
.feedback-stars button:hover {
  color: #f59e0b;
  transform: scale(1.15);
}

.feedback-modal textarea {
  width: 100%;
  padding: 0.75rem 1rem;
  background: var(--bg-input);
  border: 1.5px solid var(--border-color);
  border-radius: var(--radius-sm);
  color: var(--text-primary);
  font-size: 0.95rem;
  font-family: inherit;
  resize: vertical;
  min-height: 80px;
  outline: none;
  transition: border-color var(--transition);
  margin-bottom: 1rem;
}

.feedback-modal textarea:focus {
  border-color: var(--accent);
}

.feedback-actions {
  display: flex;
  gap: 0.75rem;
  justify-content: flex-end;
}

.feedback-actions button {
  padding: 0.5rem 1.25rem;
  border-radius: var(--radius-sm);
  font-size: 0.9rem;
  cursor: pointer;
  font-family: inherit;
  border: none;
}

.feedback-cancel {
  background: var(--bg-input);
  color: var(--text-secondary);
}

.feedback-submit {
  background: linear-gradient(135deg, var(--accent), #06b6d4);
  color: #fff;
  font-weight: 600;
}

.feedback-submit:hover {
  opacity: 0.9;
}

.feedback-thanks {
  text-align: center;
  padding: 1.5rem 0;
  color: var(--accent-green);
  font-weight: 600;
  font-size: 1.05rem;
  display: none;
}

/* ===== Page Content (About, Contact, etc.) ===== */
.page-content {
  max-width: 700px;
  margin: 0 auto;
}

.page-content h1 {
  font-size: 1.75rem;
  font-weight: 700;
  margin-bottom: 1.5rem;
}

.page-content h2 {
  font-size: 1.25rem;
  font-weight: 600;
  margin: 1.5rem 0 0.75rem;
  color: var(--accent);
}

.page-content p,
.page-content li {
  color: var(--text-secondary);
  margin-bottom: 0.75rem;
}

.page-content ul {
  padding-left: 1.5rem;
}

/* ===== Contact Form ===== */
.contact-form {
  background: var(--bg-white);
  border: 1px solid var(--border-color);
  border-radius: var(--radius);
  padding: 2rem;
  box-shadow: var(--shadow-sm);
}

.contact-form textarea {
  width: 100%;
  padding: 0.75rem 1rem;
  background: var(--bg-input);
  border: 1.5px solid var(--border-color);
  border-radius: var(--radius-sm);
  color: var(--text-primary);
  font-size: 1rem;
  font-family: inherit;
  resize: vertical;
  min-height: 120px;
  outline: none;
  transition: border-color var(--transition), box-shadow var(--transition);
}

.contact-form textarea:focus {
  border-color: var(--accent);
  box-shadow: 0 0 0 3px rgba(8, 145, 178, 0.12);
  background: var(--bg-white);
}

.btn-primary {
  display: inline-block;
  padding: 0.75rem 2rem;
  background: linear-gradient(135deg, var(--accent), #06b6d4);
  color: #fff;
  font-size: 0.95rem;
  font-weight: 600;
  border: none;
  border-radius: var(--radius-sm);
  cursor: pointer;
  transition: opacity var(--transition), transform var(--transition);
  margin-top: 1rem;
}

.btn-primary:hover {
  opacity: 0.9;
  transform: translateY(-1px);
}

/* ===== Footer ===== */
.site-footer {
  background: var(--bg-white);
  border-top: 1px solid var(--border-color);
  padding: 1.5rem;
  text-align: center;
}

.footer-links {
  list-style: none;
  display: flex;
  justify-content: center;
  gap: 1.5rem;
  margin-bottom: 0.75rem;
  flex-wrap: wrap;
}

.footer-links a {
  color: var(--text-muted);
  font-size: 0.85rem;
}

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

.footer-copy {
  color: var(--text-muted);
  font-size: 0.8rem;
}

/* ===== Mobile Nav ===== */
@media (max-width: 640px) {
  .nav-toggle {
    display: block;
  }

  .nav-links {
    display: none;
    position: absolute;
    top: 64px;
    left: 0;
    right: 0;
    background: var(--bg-white);
    border-bottom: 1px solid var(--border-color);
    flex-direction: column;
    padding: 1rem 1.5rem;
    gap: 1rem;
    box-shadow: var(--shadow);
  }

  .nav-links.open {
    display: flex;
  }

  .calculator-hero h1 {
    font-size: 1.65rem;
  }

  .results-grid {
    grid-template-columns: repeat(3, 1fr);
    gap: 0.5rem;
  }

  .result-card {
    padding: 1rem 0.5rem;
  }

  .result-value {
    font-size: 1.15rem;
  }

  .result-label {
    font-size: 0.7rem;
  }

  .result-unit {
    font-size: 0.7rem;
  }

  .calculator-card {
    padding: 1.5rem;
  }

  .articles-grid {
    grid-template-columns: 1fr;
  }
}