.particles-hub-hero {
  background-image:
    linear-gradient(
      90deg,
      rgb(255 255 255 / 97%) 0%,
      rgb(255 255 255 / 90%) 48%,
      rgb(255 255 255 / 20%) 78%
    ),
    url("../images/topics/chemistry/particles-states-and-separating-mixtures.jpg");
}

.particles-hub-hero .topic-hub-copy h1 {
  max-width: 13ch;
  font-size: clamp(2.7rem, 6vw, 5.15rem);
}

.particle-material-grid {
  grid-template-columns: minmax(0, 1fr) minmax(0, 1fr);
}

.topic-library-note {
  margin: 1.2rem 0 0;
  color: var(--navy-650);
  font-size: 0.82rem;
}

.particle-learning-page {
  background:
    radial-gradient(circle at 10% 22%, rgb(255 170 166 / 18%), transparent 28rem),
    radial-gradient(circle at 92% 82%, rgb(116 213 223 / 13%), transparent 26rem),
    var(--paper);
}

.particle-learning-page .learning-breadcrumb,
.particle-learning-page .learning-hero,
.particle-learning-page .learning-tool,
.particle-learning-page .learning-summary {
  width: min(1180px, calc(100% - 2rem));
  margin-right: auto;
  margin-left: auto;
}

.particle-learning-page .learning-breadcrumb {
  margin-top: 1.35rem;
  display: flex;
  align-items: center;
  flex-wrap: wrap;
  gap: 0.5rem;
  color: var(--navy-650);
  font-size: 0.78rem;
  font-weight: 750;
}

.particle-learning-page .learning-breadcrumb a {
  color: var(--navy-800);
  text-underline-offset: 0.2em;
}

.particle-learning-page .learning-hero {
  padding: clamp(2.25rem, 5vw, 4.5rem) 0 clamp(1.75rem, 4vw, 3rem);
}

.particle-learning-page .learning-hero h1 {
  max-width: none;
  margin: 0 0 1rem;
  font-size: clamp(2.7rem, 5vw, 4.15rem);
  letter-spacing: -0.065em;
}

.particle-learning-page .learning-intro {
  max-width: none;
  margin-bottom: 0;
  color: var(--navy-650);
  font-size: clamp(1rem, 2vw, 1.14rem);
}

.particle-explorer {
  --particle-blue: #536ecf;
  --particle-blue-deep: #304caa;
  --particle-blue-pale: #edf1ff;
  --particle-field: #edf5f8;
  --particle-panel: #fbfdfd;
}

.particle-tabs {
  padding: 0.8rem;
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 0.55rem;
  border-bottom: 1px solid var(--line);
  background: #fff7f6;
}

.particle-tab,
.particle-button-group button {
  font: inherit;
  cursor: pointer;
}

.particle-tab {
  min-height: 3.25rem;
  padding: 0.65rem 0.8rem;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.55rem;
  border: 1px solid transparent;
  border-radius: 0.9rem;
  color: var(--navy-650);
  background: transparent;
  font-size: 0.82rem;
  font-weight: 850;
}

.particle-tab > span {
  width: 1.65rem;
  height: 1.65rem;
  display: inline-grid;
  place-items: center;
  flex: 0 0 auto;
  border-radius: 50%;
  color: var(--coral-deep);
  background: #ffe1df;
  font-size: 0.68rem;
}

.particle-tab:hover {
  color: var(--navy-950);
  background: rgb(255 255 255 / 72%);
}

.particle-tab[aria-selected="true"] {
  border-color: rgb(200 86 90 / 18%);
  color: var(--navy-950);
  background: var(--surface);
  box-shadow: 0 5px 18px rgb(11 30 45 / 8%);
}

.particle-tab[aria-selected="true"] > span {
  color: white;
  background: var(--coral-deep);
}

.particle-panel {
  background:
    linear-gradient(rgb(11 30 45 / 1.8%) 1px, transparent 1px),
    linear-gradient(90deg, rgb(11 30 45 / 1.8%) 1px, transparent 1px),
    var(--particle-panel);
  background-size: 32px 32px;
}

.particle-activity-heading {
  padding: clamp(1.4rem, 3.5vw, 2.35rem) clamp(1.25rem, 3.5vw, 2.35rem) 1.1rem;
}

.particle-activity-heading h2 {
  margin: 0 0 0.45rem;
  font-size: clamp(1.75rem, 3.5vw, 2.65rem);
  letter-spacing: -0.045em;
}

.particle-activity-heading p:last-child {
  max-width: 70ch;
  margin: 0;
  color: var(--navy-650);
  font-size: 0.9rem;
}

.particle-controls {
  padding: 0 clamp(1.25rem, 3.5vw, 2.35rem) 1.35rem;
  display: flex;
  align-items: end;
  justify-content: space-between;
  gap: 1.25rem;
}

.particle-controls fieldset {
  min-width: 0;
  margin: 0;
  padding: 0;
  border: 0;
}

.particle-controls legend {
  margin-bottom: 0.55rem;
  color: var(--navy-650);
  font-size: 0.69rem;
  font-weight: 900;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.particle-button-group {
  display: flex;
  flex-wrap: wrap;
  gap: 0.45rem;
}

.particle-button-group button {
  min-height: 2.55rem;
  padding: 0.55rem 0.85rem;
  border: 1px solid var(--line);
  border-radius: 0.75rem;
  color: var(--navy-650);
  background: var(--surface);
  font-size: 0.78rem;
  font-weight: 850;
}

.particle-button-group button:hover {
  border-color: var(--particle-blue);
  color: var(--navy-950);
}

.particle-button-group button[aria-pressed="true"] {
  border-color: var(--particle-blue);
  color: var(--particle-blue-deep);
  background: var(--particle-blue-pale);
  box-shadow: inset 0 0 0 1px rgb(83 110 207 / 12%);
}

.particle-view-grid {
  padding: 0 clamp(1.25rem, 3.5vw, 2.35rem);
  display: grid;
  grid-template-columns: minmax(0, 0.9fr) minmax(0, 1.1fr);
  gap: 1rem;
}

.particle-view-card {
  min-width: 0;
  overflow: hidden;
  border: 1px solid var(--line);
  border-radius: var(--radius-medium);
  background: var(--surface);
  box-shadow: 0 10px 28px rgb(11 30 45 / 6%);
}

.particle-view-card > header {
  min-height: 3.25rem;
  padding: 0.75rem 0.95rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 0.8rem;
  border-bottom: 1px solid var(--line);
}

.particle-view-card h3 {
  margin: 0;
  font-size: 0.92rem;
}

.particle-stage {
  min-height: 340px;
  position: relative;
  overflow: hidden;
  background: var(--particle-field);
}

.observable-stage {
  min-height: 340px;
  overflow: hidden;
  background: var(--particle-field);
}

.observable-stage img {
  width: 100%;
  height: 340px;
  display: block;
  object-fit: cover;
  object-position: center;
}

.particle-dot {
  width: 38px;
  height: 38px;
  position: absolute;
  border: 3px solid #31499d;
  border-radius: 50%;
  background: #7187df;
  box-shadow: inset -5px -5px 0 rgb(31 48 112 / 20%);
}

.particle-stage[data-motion="vibrate"] .particle-dot,
.comparison-stage[data-motion="vibrate"] .particle-dot {
  animation: particle-vibrate var(--vibrate-duration, 520ms) ease-in-out infinite alternate;
  animation-delay: var(--vibrate-delay, 0ms);
}

.particle-stage[data-motion="slide"] .particle-dot,
.comparison-stage[data-motion="slide"] .particle-dot {
  animation: particle-liquid-move var(--liquid-duration, 1450ms) linear infinite;
  animation-delay: var(--liquid-delay, 0ms);
}

.particle-stage[data-motion="fast"] .particle-dot,
.comparison-stage[data-motion="fast"] .particle-dot {
  animation: particle-gas-flight var(--gas-duration, 2200ms) linear infinite;
  animation-delay: var(--gas-delay, 0ms);
}

.particle-explanation {
  margin: 1rem clamp(1.25rem, 3.5vw, 2.35rem) 0;
  padding: 1rem 1.15rem;
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  align-items: center;
  gap: 1rem;
  border: 1px solid #d8dff7;
  border-radius: 1rem;
  background: var(--particle-blue-pale);
}

.particle-explanation strong {
  color: var(--particle-blue-deep);
  font-size: 0.72rem;
  letter-spacing: 0.05em;
  text-transform: uppercase;
}

.particle-explanation p {
  margin: 0.25rem 0 0;
  color: var(--navy-650);
  font-size: 0.84rem;
}

.particle-panel {
  padding-bottom: clamp(1.5rem, 4vw, 2.5rem);
}

.particle-comparison-grid {
  padding: 0 clamp(1.25rem, 3.5vw, 2.35rem);
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 0.9rem;
}

.comparison-card {
  min-width: 0;
  overflow: hidden;
  border: 1px solid var(--line);
  border-radius: var(--radius-medium);
  background: var(--surface);
  box-shadow: 0 8px 25px rgb(11 30 45 / 6%);
}

.comparison-card h3 {
  margin: 0;
  padding: 0.9rem 1rem;
  font-size: 1.1rem;
}

.comparison-stage {
  height: 190px;
  position: relative;
  overflow: hidden;
  border-top: 1px solid var(--line);
  border-bottom: 1px solid var(--line);
  background: var(--particle-field);
}

.comparison-stage .particle-dot {
  width: 28px;
  height: 28px;
  border-width: 2px;
}

.comparison-facts {
  margin: 0;
  padding: 0.9rem 1rem 1.05rem;
  display: grid;
  grid-template-columns: auto 1fr;
  gap: 0.55rem 0.7rem;
  font-size: 0.75rem;
}

.comparison-facts dt {
  color: var(--navy-650);
}

.comparison-facts dd {
  margin: 0;
  font-weight: 800;
  text-align: right;
}

.particle-explorer button:focus-visible,
.particle-learning-page .learning-breadcrumb a:focus-visible {
  outline: 3px solid var(--aqua-deep);
  outline-offset: 3px;
}

@keyframes particle-vibrate {
  from { transform: translate(var(--vibrate-from-x, -1.5px), var(--vibrate-from-y, -1px)); }
  to { transform: translate(var(--vibrate-to-x, 1.5px), var(--vibrate-to-y, 1px)); }
}

@keyframes particle-liquid-move {
  0%, 100% { transform: translate(0, 0); }
  12% { transform: translate(var(--liquid-x-1, 7px), var(--liquid-y-1, -5px)); }
  25% { transform: translate(var(--liquid-x-2, -8px), var(--liquid-y-2, 4px)); }
  37% { transform: translate(var(--liquid-x-3, 5px), var(--liquid-y-3, 8px)); }
  50% { transform: translate(var(--liquid-x-4, -6px), var(--liquid-y-4, -7px)); }
  62% { transform: translate(var(--liquid-x-5, 9px), var(--liquid-y-5, 2px)); }
  75% { transform: translate(var(--liquid-x-6, -3px), var(--liquid-y-6, 9px)); }
  87% { transform: translate(var(--liquid-x-7, 4px), var(--liquid-y-7, -8px)); }
  94% { transform: translate(var(--liquid-x-8, -7px), var(--liquid-y-8, -2px)); }
}

@keyframes particle-gas-flight {
  0%, 100% { transform: translate(0, 0); }
  14% { transform: translate(var(--gas-x-1, 18px), var(--gas-y-1, -12px)); }
  29% { transform: translate(var(--gas-x-2, -20px), var(--gas-y-2, 16px)); }
  44% { transform: translate(var(--gas-x-3, 12px), var(--gas-y-3, 22px)); }
  59% { transform: translate(var(--gas-x-4, -18px), var(--gas-y-4, -20px)); }
  74% { transform: translate(var(--gas-x-5, 24px), var(--gas-y-5, 8px)); }
  88% { transform: translate(var(--gas-x-6, -10px), var(--gas-y-6, 18px)); }
}

@media (max-width: 850px) {
  .particle-view-grid {
    grid-template-columns: 1fr;
  }

  .particle-comparison-grid {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }

  .particle-material-grid {
    grid-template-columns: 1fr;
  }
}

@media (max-width: 680px) {
  .particle-controls {
    align-items: stretch;
    flex-direction: column;
  }

  .particle-explanation {
    grid-template-columns: 1fr;
  }

  .particle-comparison-grid {
    grid-template-columns: 1fr;
  }
}

@media (max-width: 520px) {
  .particle-learning-page .learning-hero h1 {
    font-size: clamp(2.55rem, 13vw, 4rem);
  }

  .particles-hub-hero .topic-hub-copy h1 {
    font-size: clamp(2.3rem, 12vw, 3.6rem);
  }

  .particle-tabs {
    padding: 0.55rem;
    gap: 0.3rem;
  }

  .particle-tab {
    padding: 0.55rem 0.3rem;
    flex-direction: column;
    gap: 0.25rem;
    font-size: 0.68rem;
    text-align: center;
  }

  .particle-tab > span {
    width: 1.4rem;
    height: 1.4rem;
  }

  .observable-stage,
  .particle-stage {
    min-height: 285px;
  }

  .observable-stage img {
    height: 285px;
  }
}

@media (prefers-reduced-motion: reduce) {
  .particle-dot {
    animation: none !important;
    transition: none !important;
  }
}