body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Helvetica, Arial, sans-serif;
  margin: 0;
  padding: 0;
  background: #eee;
  color: #222;
}

:root {
  --accent: #2678A5;
  --accent-soft: rgba(38, 120, 165, 0.35);
  --accent-strong: rgba(38, 120, 165, 0.8);
  --text: #222;
  --muted: #666;
  --surface: #ddd;
}

.language-bar {
  background: var(--accent);
  color: #fff;
  font-size: 0.85rem;
}

.language-inner {
  max-width: 760px;
  margin: auto;
  padding: 6px 20px;
  text-align: right;
}

.language-inner a {
  color: #fff;
  text-decoration: none;
  margin-left: 10px;
  font-weight: 500;
}

.language-inner a:hover {
  text-decoration: underline;
}

header {
  text-align: center;
  padding: 72px 20px 54px 20px;
}

.site-kicker {
  margin: 0 0 10px 0;
  color: var(--muted);
  font-size: 1.4rem;
  letter-spacing: 0.03em;
  text-transform: uppercase;
}

h1 {
  font-size: 2.55rem;
  letter-spacing: 0.02em;
  margin: 6px 0 10px 0;
  color: var(--accent);
  font-weight: 600;
}

h2 {
  margin-bottom: 18px;
}

h3 {
  margin: 0 0 10px 0;
  font-size: 1.35rem;
  color: var(--accent);
  font-weight: 600;
}

.tagline {
  margin-top: 6px;
  color: var(--muted);
  font-size: 1.1rem;
}

.book-cover {
  width: 320px;
  max-width: 100%;
  height: auto;
  display: block;
  margin: 0 auto 34px auto;
}

main {
  max-width: 760px;
  margin: auto;
  padding: 20px;
}

section {
  max-width: 800px;
  margin: 60px auto;
  padding: 0 20px;
}

.book-intro,
.placeholder-section,
.backlink,
.faq,
.research-architecture,
#impressum,
#datenschutz {
  max-width: 720px;
  margin: 60px auto;
  padding: 0 20px;
  text-align: justify;
  hyphens: auto;
}

.book-intro p,
.placeholder-section p,
.backlink p,
.faq p,
.research-architecture p,
#impressum p,
#datenschutz p {
  letter-spacing: -0.02em;
  line-height: 1.7;
  margin: 0 0 16px 0;
  color: #333;
}

.book-meta {
  margin: 0 0 22px 0;
  color: var(--muted);
  font-size: 0.98rem;
  line-height: 1.5;
}

.buy-note {
  margin-top: 24px;
  padding-left: 14px;
  border-left: 3px solid var(--accent);
}

/* FAQ */

.faq {
  margin-top: 64px;
}

.faq-intro {
  margin-bottom: 34px;
}

.faq h3 {
  font-size: calc(1.35rem - 2pt);
  margin: 38px 0 14px 0;
  color: var(--accent);
  font-weight: 600;
}

.faq h3:first-of-type {
  margin-top: 28px;
}

.faq details {
  margin: 0 0 12px 0;
  padding: 0;
  border-bottom: 1px solid #d4d4d4;
}

.faq summary {
  cursor: pointer;
  font-weight: 500;
  font-size: 1.02rem;
  line-height: 1.5;
  letter-spacing: -0.01em;
  color: #2b2b2b;
  padding: 10px 0 11px 0;
}

.faq summary::marker {
  color: var(--muted);
}

.faq summary:hover {
  color: var(--accent);
}

.faq details[open] summary {
  color: var(--accent);
  padding-bottom: 8px;
}

.faq details p {
  margin: 0 0 18px 0;
  padding: 0 0 2px 0;
}

/* Research Architecture */

.research-architecture {
  margin-top: 64px;
}

.research-architecture-intro {
  margin-bottom: 34px;
}

.research-architecture h3 {
  font-size: calc(1.35rem - 2pt);
  margin: 38px 0 14px 0;
  color: var(--accent);
  font-weight: 600;
}

.research-architecture h3:first-of-type {
  margin-top: 28px;
}

.research-architecture details {
  margin: 0 0 12px 0;
  padding: 0;
  border-bottom: 1px solid #d4d4d4;
}

.research-architecture summary {
  cursor: pointer;
  font-weight: 500;
  font-size: 1.02rem;
  line-height: 1.5;
  letter-spacing: -0.01em;
  color: #2b2b2b;
  padding: 10px 0 11px 0;
}

.research-architecture summary::marker {
  color: var(--muted);
}

.research-architecture summary:hover {
  color: var(--accent);
}

.research-architecture details[open] summary {
  color: var(--accent);
  padding-bottom: 8px;
}

.research-architecture details p {
  margin: 0 0 18px 0;
  padding: 0 0 2px 0;
}

.paper-list {
  margin: 14px 0 26px 0;
  padding-left: 1.4em;
}

.paper-list li {
  margin: 0 0 8px 0;
  line-height: 1.6;
}

.paper-list li::marker {
  color: var(--muted);
}

code {
  background: #e2e2e2;
  padding: 0.1em 0.28em;
  border-radius: 4px;
  font-size: 0.95em;
}

a {
  color: #444;
  text-decoration: underline;
  text-decoration-color: var(--accent-soft);
  text-underline-offset: 2px;
}

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


.social {
  display: flex;
  justify-content: center;
  gap: 18px;
  margin-top: 24px;
}

.social a {
  display: inline-flex;
  width: 38px;
  height: 38px;
  align-items: center;
  justify-content: center;
  border: 1px solid var(--accent);
  border-radius: 50%;
  transition: all 0.2s ease;
}

.social a:hover {
  background: var(--accent);
}

.social img {
  width: 21px;
  height: 21px;
  filter: invert(17%);
}

.social a:hover img {
  filter: invert(1);
}

footer {
  max-width: 720px;
  margin: 0 auto;
  padding: 30px 20px;
  text-align: center;
  color: var(--muted);
  box-sizing: border-box;
}

footer p {
  line-height: 1.6;
}

.legal-separator {
  border: none;
  border-top: 1px solid #d3d3d3;
  margin: 60px auto 30px auto;
  max-width: 720px;
}

.identifiers {
  margin-top: 14px;
  font-size: 0.85rem;
  color: #555;
}

@media (max-width: 560px) {
  header {
    padding: 52px 18px 36px 18px;
  }

  h1 {
    font-size: 2.05rem;
  }

  main {
    padding: 10px;
  }

  .book-intro,
  .placeholder-section,
  .backlink,
  .faq,
  .research-architecture,
  #impressum,
  #datenschutz {
    margin: 44px auto;
    padding: 0 14px;
    text-align: left;
  }

  .faq h3,
  .research-architecture h3 {
    margin-top: 34px;
    margin-bottom: 12px;
  }
}