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

body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Oxygen,
    Ubuntu, sans-serif;
  line-height: 1.6;
  color: #333;
  background: #fff;
}

body.dark {
  color: #e0e0e0;
  background: #1e1e1e;
}

/* Header */
.site-header {
  padding: 6px 20px;
  border-bottom: 1px solid #e5e7eb;
  background: #fff;
  position: sticky;
  top: 0;
  z-index: 100;
  box-shadow: 0 1px 3px rgba(0, 0, 0, 0.04);
}

body.dark .site-header {
  border-bottom-color: #444;
  background: #252525;
  box-shadow: 0 1px 3px rgba(0, 0, 0, 0.2);
}

.header-inner {
  max-width: 1100px;
  margin: 0 auto;
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.logo {
  font-size: 1.5rem;
  font-weight: 700;
  color: #1976d2;
  text-decoration: none;
  letter-spacing: -0.02em;
}

.logo:hover {
  color: #1565c0;
}

body.dark .logo {
  color: #42a5f5;
}

body.dark .logo:hover {
  color: #64b5f6;
}

.header-nav {
  display: flex;
  align-items: center;
  gap: 12px;
}

.btn-login,
.btn-home,
.btn-wall,
.btn-profile {
  display: inline-block;
  padding: 10px 20px;
  background: #1976d2;
  color: #fff;
  border: none;
  border-radius: 8px;
  font-weight: 600;
  font-size: 0.95rem;
  cursor: pointer;
  text-decoration: none;
  transition: background 0.2s, transform 0.2s;
  box-shadow: 0 2px 6px rgba(25, 118, 210, 0.35);
}

.btn-login:hover,
.btn-home:hover,
.btn-wall:hover,
.btn-profile:hover {
  background: #1565c0;
  transform: translateY(-1px);
}

body.dark .btn-login,
body.dark .btn-home,
body.dark .btn-wall,
body.dark .btn-profile {
  background: #1e88e5;
  box-shadow: 0 2px 6px rgba(30, 136, 229, 0.4);
}

body.dark .btn-login:hover,
body.dark .btn-home:hover,
body.dark .btn-wall:hover,
body.dark .btn-profile:hover {
  background: #1976d2;
}

.btn-logout {
  display: inline-block;
  padding: 10px 20px;
  border-radius: 8px;
  font-weight: 600;
  font-size: 0.95rem;
  cursor: pointer;
  text-decoration: none;
  transition: background 0.2s, transform 0.2s;
  background: #c62828;
  color: #fff;
  box-shadow: 0 2px 6px rgba(198, 40, 40, 0.35);
}

.btn-logout:hover {
  background: #b71c1c;
  transform: translateY(-1px);
}

body.dark .btn-logout {
  background: #e53935;
}

body.dark .btn-logout:hover {
  background: #c62828;
}

.theme-wrap {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0;
}

.theme-toggle {
  width: 44px;
  height: 44px;
  border: none;
  border-radius: 50%;
  cursor: pointer;
  font-size: 22px;
  display: flex;
  align-items: center;
  justify-content: center;
  background: #1976d2;
  color: #fff;
  box-shadow: 0 2px 8px rgba(25, 118, 210, 0.4);
  transition: transform 0.2s, box-shadow 0.2s;
}

body.dark .theme-toggle {
  background: #f57c00;
  box-shadow: 0 2px 8px rgba(245, 124, 0, 0.4);
}

.theme-toggle:hover {
  transform: translateY(-2px);
  box-shadow: 0 4px 12px rgba(25, 118, 210, 0.45);
}

body.dark .theme-toggle:hover {
  box-shadow: 0 4px 12px rgba(245, 124, 0, 0.5);
}

/* Hero */
.hero {
  max-width: 800px;
  margin: 0 auto;
  padding: 80px 24px 60px;
  text-align: center;
}

.hero-tagline {
  font-size: 1.25rem;
  color: #666;
  margin-bottom: 8px;
  font-weight: 500;
}

body.dark .hero-tagline {
  color: #aaa;
}

.hero-title {
  font-size: clamp(2.5rem, 6vw, 3.5rem);
  font-weight: 800;
  color: #111;
  letter-spacing: -0.03em;
  line-height: 1.15;
  margin-bottom: 16px;
}

body.dark .hero-title {
  color: #fff;
}

.hero-subtitle {
  font-size: 1.15rem;
  color: #555;
  max-width: 560px;
  margin: 0 auto;
}

body.dark .hero-subtitle {
  color: #bbb;
}

/* Features */
.features {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(260px, 1fr));
  gap: 24px;
  align-items: stretch;
  max-width: 1100px;
  margin: 0 auto;
  padding: 40px 24px 60px;
}

.feature-card {
  background: #f8fafc;
  border: 1px solid #e2e8f0;
  border-radius: 16px;
  padding: 40px;
  margin: 0;
  min-width: 0;
  box-shadow: 0 4px 20px rgba(0, 0, 0, 0.06);
  display: flex;
  flex-direction: column;
}

body.dark .feature-card {
  background: #2d2d2d;
  border-color: #444;
  box-shadow: 0 4px 20px rgba(0, 0, 0, 0.3);
}

.feature-card .btn-primary {
  margin-top: auto;
  align-self: flex-start;
}

.feature-title {
  font-size: 1.75rem;
  font-weight: 700;
  color: #1976d2;
  margin-bottom: 16px;
}

.feature-desc {
  color: #444;
  margin-bottom: 24px;
  font-size: 1.05rem;
}

body.dark .feature-desc {
  color: #ccc;
}

.btn-primary {
  display: inline-block;
  padding: 14px 28px;
  background: #1976d2;
  color: #fff !important;
  text-decoration: none;
  border-radius: 10px;
  font-weight: 600;
  font-size: 1rem;
  transition: background 0.2s, transform 0.2s, box-shadow 0.2s;
  box-shadow:
    0 2px 0 rgba(255, 255, 255, 0.2) inset,
    0 4px 12px rgba(25, 118, 210, 0.35);
}

.btn-primary:hover {
  background: #1565c0;
  transform: translateY(-2px);
  box-shadow:
    0 2px 0 rgba(255, 255, 255, 0.25) inset,
    0 6px 20px rgba(25, 118, 210, 0.4);
}

/* About */
.about {
  max-width: 700px;
  margin: 0 auto;
  padding: 50px 24px 60px;
}

.section-title {
  font-size: 1.75rem;
  font-weight: 700;
  color: #111;
  margin-bottom: 24px;
  text-align: center;
}

body.dark .section-title {
  color: #fff;
}

.about-text {
  color: #444;
  margin-bottom: 16px;
  font-size: 1.05rem;
}

body.dark .about-text {
  color: #ccc;
}

.about-text code {
  background: #f1f5f9;
  padding: 2px 8px;
  border-radius: 6px;
  font-size: 0.95em;
}

body.dark .about-text code {
  background: #444;
  color: #e0e0e0;
}

/* How it works */
.how-it-works {
  max-width: 1100px;
  margin: 0 auto;
  padding: 50px 24px 60px;
  background: #f8fafc;
}

body.dark .how-it-works {
  background: #252525;
}

.how-it-works .section-title {
  margin-bottom: 40px;
}

.steps {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(260px, 1fr));
  gap: 32px;
}

.step {
  background: #fff;
  border-radius: 12px;
  padding: 28px;
  border: 1px solid #e2e8f0;
  box-shadow: 0 2px 10px rgba(0, 0, 0, 0.04);
}

body.dark .step {
  background: #2d2d2d;
  border-color: #444;
  box-shadow: 0 2px 10px rgba(0, 0, 0, 0.3);
}

.step-num {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 40px;
  height: 40px;
  background: #1976d2;
  color: #fff;
  font-weight: 700;
  font-size: 1.25rem;
  border-radius: 10px;
  margin-bottom: 16px;
}

.step h3 {
  font-size: 1.2rem;
  color: #111;
  margin-bottom: 8px;
}

body.dark .step h3 {
  color: #fff;
}

.step p {
  color: #555;
  font-size: 0.95rem;
}

body.dark .step p {
  color: #ccc;
}

.step p code {
  background: #f1f5f9;
  padding: 2px 6px;
  border-radius: 4px;
  font-size: 0.9em;
}

body.dark .step p code {
  background: #444;
  color: #e0e0e0;
}

/* Why */
.why {
  max-width: 700px;
  margin: 0 auto;
  padding: 50px 24px 60px;
}

.why-list {
  list-style: none;
}

.why-list li {
  padding: 14px 0;
  padding-left: 32px;
  position: relative;
  color: #444;
  font-size: 1.05rem;
}

body.dark .why-list li {
  color: #ccc;
}

.why-list li::before {
  content: "✓";
  position: absolute;
  left: 0;
  color: #1976d2;
  font-weight: 700;
  font-size: 1.2rem;
}

/* FAQ */
.faq {
  max-width: 700px;
  margin: 0 auto;
  padding: 50px 24px 60px;
  background: #f8fafc;
}

body.dark .faq {
  background: #252525;
}

.faq .section-title {
  margin-bottom: 32px;
}

.faq-list {
  display: flex;
  flex-direction: column;
  gap: 24px;
}

.faq-item {
  display: flex;
  gap: 16px;
  align-items: flex-start;
}

.faq-icon {
  flex-shrink: 0;
  width: 40px;
  height: 40px;
  display: flex;
  align-items: center;
  justify-content: center;
  color: #1976d2;
}

body.dark .faq-icon {
  color: #42a5f5;
}

.faq-icon svg {
  width: 28px;
  height: 28px;
}

.faq-content {
  flex: 1;
  min-width: 0;
}

.faq-q {
  font-weight: bold;
  font-size: 1.05rem;
  color: #111;
  margin-bottom: 8px;
}

body.dark .faq-q {
  color: #fff;
}

.faq-a {
  font-size: 0.98rem;
  color: #444;
  line-height: 1.55;
  margin: 0;
}

body.dark .faq-a {
  color: #ccc;
}

/* CTA */
.cta {
  text-align: center;
  padding: 40px 24px 60px;
}

.cta-buttons {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  align-items: center;
  gap: 12px;
}

.btn-large {
  padding: 18px 36px;
  font-size: 1.1rem;
}

/* Footer */
.site-footer {
  text-align: center;
  padding: 24px;
  border-top: 1px solid #e5e7eb;
  color: #666;
  font-size: 0.95rem;
}

body.dark .site-footer {
  border-top-color: #444;
  color: #888;
}

/* Responsive: tablet and below */
@media (max-width: 768px) {
  .site-header {
    padding: 6px 16px;
  }

  .header-inner {
    flex-wrap: wrap;
  }

  .logo {
    font-size: 1.35rem;
  }

  .hero {
    padding: 50px 20px 45px;
  }

  .hero-tagline {
    font-size: 1.1rem;
  }

  .hero-title {
    font-size: clamp(2rem, 5vw, 2.75rem);
  }

  .hero-subtitle {
    font-size: 1rem;
  }

  .features,
  .about,
  .how-it-works,
  .why,
  .cta {
    padding-left: 16px;
    padding-right: 16px;
  }

  .features {
    grid-template-columns: 1fr;
    gap: 20px;
  }

  .feature-card {
    padding: 28px 24px;
  }

  .feature-title {
    font-size: 1.5rem;
  }

  .section-title {
    font-size: 1.5rem;
  }

  .steps {
    grid-template-columns: 1fr;
    gap: 24px;
  }

  .btn-primary,
  .btn-large {
    padding: 12px 24px;
    font-size: 0.95rem;
  }
}

/* Responsive: mobile */
@media (max-width: 600px) {
  .site-header {
    padding: 4px 12px;
  }

  .header-nav {
    gap: 12px;
  }

  .logo {
    font-size: 1.25rem;
  }

  .btn-login,
  .btn-home,
  .btn-wall,
  .btn-profile,
  .btn-logout {
    padding: 8px 16px;
    font-size: 0.9rem;
  }

  .theme-toggle {
    width: 40px;
    height: 40px;
    font-size: 18px;
  }

  .hero {
    padding: 36px 16px 32px;
  }

  .hero-tagline {
    font-size: 1rem;
  }

  .hero-subtitle {
    font-size: 0.95rem;
  }

  .feature-card {
    padding: 24px 20px;
  }

  .feature-title {
    font-size: 1.35rem;
  }

  .feature-desc {
    font-size: 0.95rem;
  }

  .about,
  .how-it-works,
  .why {
    padding-top: 36px;
    padding-bottom: 44px;
  }

  .about-text {
    font-size: 0.95rem;
  }

  .step {
    padding: 22px 20px;
  }

  .step-num {
    width: 36px;
    height: 36px;
    font-size: 1.1rem;
  }

  .step h3 {
    font-size: 1.1rem;
  }

  .step p {
    font-size: 0.9rem;
  }

  .why-list li {
    font-size: 0.95rem;
    padding: 12px 0 12px 28px;
  }

  .cta {
    padding: 32px 16px 44px;
  }

  .site-footer {
    padding: 20px 16px;
    font-size: 0.9rem;
  }
}

/* Responsive: small mobile */
@media (max-width: 380px) {
  .header-inner {
    justify-content: center;
    flex-direction: column;
    gap: 12px;
  }

  .header-nav {
    width: 100%;
    justify-content: center;
  }

  .hero-title {
    font-size: 1.75rem;
  }
}