:root {
  --bg: #0f172a;
  --bg-alt: #111c31;
  --primary: #58a6ff;
  --primary-muted: rgba(88, 166, 255, 0.16);
  --text: #e7ecf7;
  --text-muted: #94a3b8;
  --border: #1f2a40;
  --shadow: 0 20px 45px rgba(8, 15, 31, 0.38);
  font-size: 16px;
}

*,
*::before,
*::after {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: "Inter", -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  background: radial-gradient(circle at 20% 20%, rgba(88, 166, 255, 0.12), transparent 55%),
    radial-gradient(circle at 80% 0%, rgba(124, 58, 237, 0.18), transparent 60%), var(--bg);
  color: var(--text);
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}

.top-bar {
  padding: 2.5rem clamp(1.5rem, 4vw, 3.5rem);
  background: radial-gradient(circle at top left, rgba(88, 166, 255, 0.35), transparent 45%),
    radial-gradient(circle at top right, rgba(56, 189, 248, 0.28), transparent 55%),
    linear-gradient(160deg, #0b1220, #111c31);
  color: #ffffff;
}

.branding h1 {
  margin: 0 0 0.75rem;
  font-size: clamp(2rem, 4vw, 2.75rem);
  letter-spacing: 0.02em;
}

.branding p {
  margin: 0;
  max-width: 32rem;
  font-size: clamp(1rem, 2.4vw, 1.1rem);
  line-height: 1.6;
}

.layout {
  display: grid;
  grid-template-columns: minmax(220px, 280px) 1fr;
  gap: clamp(1.5rem, 3vw, 2.5rem);
  padding: clamp(1.5rem, 4vw, 3rem);
  max-width: 1200px;
  width: 100%;
  margin: 0 auto;
  flex: 1;
}

.chemical-list {
  background: rgba(17, 28, 49, 0.92);
  border-radius: 20px;
  padding: 1.5rem;
  box-shadow: var(--shadow);
  align-self: start;
  border: 1px solid var(--border);
}

.chemical-list h2 {
  margin: 0 0 1.25rem;
  font-size: 1.05rem;
  letter-spacing: 0.04em;
  text-transform: uppercase;
  color: var(--text-muted);
}

.chemical-list ul {
  list-style: none;
  margin: 0;
  padding: 0;
  display: grid;
  gap: 0.75rem;
}

.chemical-list button {
  width: 100%;
  border: 1px solid transparent;
  background: rgba(15, 23, 42, 0.75);
  color: var(--text);
  padding: 0.85rem 1rem;
  border-radius: 14px;
  text-align: left;
  font-size: 0.98rem;
  font-weight: 500;
  cursor: pointer;
  transition: transform 140ms ease, box-shadow 140ms ease, border 140ms ease, background 140ms ease;
}

.chemical-list button:hover {
  transform: translateY(-2px);
  box-shadow: 0 10px 30px rgba(88, 166, 255, 0.18);
  border-color: rgba(88, 166, 255, 0.65);
  background: rgba(88, 166, 255, 0.12);
}

.chemical-list button:focus-visible {
  outline: 3px solid rgba(88, 166, 255, 0.45);
  outline-offset: 2px;
}

.chemical-list button.active {
  border-color: var(--primary);
  background: var(--primary-muted);
  color: var(--primary);
  box-shadow: 0 12px 32px rgba(88, 166, 255, 0.28);
}

.content-area {
  display: grid;
  gap: clamp(1.5rem, 3vw, 2.5rem);
}

.content-header {
  background: rgba(15, 23, 42, 0.85);
  border-radius: 20px;
  padding: clamp(1.5rem, 3vw, 2rem);
  box-shadow: var(--shadow);
  display: grid;
  gap: 0.75rem;
  border: 1px solid var(--border);
}

.content-header-top {
  display: flex;
  align-items: center;
  gap: 0.85rem;
  flex-wrap: wrap;
}

.content-header h2 {
  margin: 0;
  font-size: clamp(1.5rem, 3vw, 2rem);
}

.content-header p {
  margin: 0;
  color: var(--text-muted);
  line-height: 1.6;
}

.content-sections {
  display: grid;
  gap: clamp(1.25rem, 3vw, 1.75rem);
}

.content-card {
  background: rgba(15, 23, 42, 0.82);
  border-radius: 20px;
  padding: clamp(1.5rem, 3vw, 2rem);
  box-shadow: var(--shadow);
  display: grid;
  gap: 1rem;
  transition: transform 200ms ease, box-shadow 200ms ease, border 200ms ease;
  border: 1px solid var(--border);
}

.content-card h3 {
  margin: 0;
  font-size: 1.1rem;
  letter-spacing: 0.03em;
  text-transform: uppercase;
  color: var(--text-muted);
}

.content-card:hover {
  transform: translateY(-4px);
  box-shadow: 0 28px 55px rgba(8, 15, 31, 0.45);
  border-color: rgba(88, 166, 255, 0.35);
}

.video-wrapper {
  position: relative;
  width: 100%;
  background: linear-gradient(160deg, rgba(88, 166, 255, 0.22), rgba(14, 116, 144, 0.14));
  border-radius: 16px;
  overflow: hidden;
  padding: clamp(0.75rem, 2.5vw, 1.25rem);
  color: var(--text-muted);
}

.video-wrapper video {
  display: block;
  width: 100%;
  height: auto;
  max-height: 540px;
  border-radius: 12px;
  background: #020617;
  object-fit: contain;
}

.video-wrapper p {
  margin: 0.5rem 0 0;
  text-align: center;
}

.article-wrapper {
  display: grid;
  gap: 0.75rem;
  color: var(--text);
  line-height: 1.7;
}

.content-line {
  margin: 0;
  padding: 0.75rem 0.9rem;
  border-radius: 12px;
  background: rgba(15, 23, 42, 0.65);
  border: 1px solid var(--border);
  color: var(--text);
  font-weight: 500;
}

.content-button {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.4rem;
  width: fit-content;
  margin: 0;
  padding: 0.55rem 1.1rem;
  border-radius: 999px;
  background: var(--primary);
  color: #0b1220;
  font-weight: 600;
  text-decoration: none;
  border: none;
  transition: transform 140ms ease, box-shadow 140ms ease, background 140ms ease;
}

.content-button:hover,
.content-button:focus-visible {
  transform: translateY(-2px);
  box-shadow: 0 12px 28px rgba(88, 166, 255, 0.35);
  background: #7ec0ff;
  color: #020617;
}

.content-header-top .content-button {
  padding: 0.5rem 1rem;
}

.footer {
  text-align: center;
  padding: 2rem 1rem 2.5rem;
  font-size: 0.95rem;
  color: var(--text-muted);
}

@media (max-width: 960px) {
  .layout {
    grid-template-columns: 1fr;
  }

  .chemical-list {
    position: sticky;
    top: 1.5rem;
    z-index: 2;
  }
}

@media (max-width: 640px) {
  .top-bar {
    padding: 2rem 1.5rem;
  }

  .layout {
    padding: 1.5rem clamp(1rem, 6vw, 1.75rem) 2.5rem;
  }

  .chemical-list {
    position: static;
  }

  .video-wrapper {
    min-height: 200px;
  }
}