:root {
  font-family: Inter, system-ui, Arial, sans-serif;
  --lumen-black-blue: #070b1a;
  --lumen-violet: #8b5cf6;
  --lumen-neon-cyan: #00f5ff;
  --lumen-nebula-gray: #8f9bad;
  --lumen-white: #ffffff;

  color: var(--lumen-white);
  background: radial-gradient(
    circle at 20% 20%,
    #111a38 0%,
    var(--lumen-black-blue) 48%,
    #050812 100%
  );
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  min-height: 100vh;
  position: relative;
  overflow-x: hidden;
}

body::before,
body::after {
  content: "";
  position: fixed;
  width: 360px;
  height: 360px;
  border-radius: 50%;
  z-index: -1;
  filter: blur(60px);
  pointer-events: none;
}

body::before {
  top: -120px;
  left: -120px;
  background: color-mix(in srgb, var(--lumen-violet) 55%, transparent);
}

body::after {
  bottom: -140px;
  right: -100px;
  background: color-mix(in srgb, var(--lumen-neon-cyan) 45%, transparent);
}

.loading-overlay {
  position: fixed;
  inset: 0;
  display: flex;
  align-items: center;
  justify-content: center;
  background: color-mix(in srgb, var(--lumen-black-blue) 78%, transparent);
  backdrop-filter: blur(6px);
  z-index: 1000;
}

.loading-card {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 12px;
  padding: 20px 24px;
  border-radius: 14px;
  border: 1px solid color-mix(in srgb, var(--lumen-neon-cyan) 35%, transparent);
  background: color-mix(in srgb, var(--lumen-black-blue) 84%, #1a2958 16%);
  box-shadow: 0 18px 40px color-mix(in srgb, var(--lumen-black-blue) 75%, black);
}

.spinner {
  width: 34px;
  height: 34px;
  border: 3px solid color-mix(in srgb, var(--lumen-nebula-gray) 40%, transparent);
  border-top-color: var(--lumen-neon-cyan);
  border-radius: 50%;
  animation: spin 0.9s linear infinite;
}

@keyframes spin {
  to {
    transform: rotate(360deg);
  }
}

.container {
  max-width: 1040px;
  margin: 0 auto;
  padding: 24px 16px 40px;
}

.menu-toggle {
  position: fixed;
  top: 18px;
  left: 18px;
  width: 46px;
  height: 46px;
  margin: 0;
  border-radius: 12px;
  font-size: 1.35rem;
  z-index: 900;
  box-shadow: 0 8px 20px color-mix(in srgb, var(--lumen-black-blue) 70%, black);
}

.drawer-backdrop {
  position: fixed;
  inset: 0;
  background: color-mix(in srgb, var(--lumen-black-blue) 68%, transparent);
  backdrop-filter: blur(3px);
  z-index: 940;
}

.session-drawer {
  position: fixed;
  top: 0;
  left: 0;
  width: min(380px, 92vw);
  height: 100vh;
  padding: 18px 16px;
  border-right: 1px solid color-mix(in srgb, var(--lumen-nebula-gray) 35%, transparent);
  background: color-mix(in srgb, var(--lumen-black-blue) 84%, #16234f 16%);
  box-shadow: 20px 0 40px color-mix(in srgb, var(--lumen-black-blue) 75%, black);
  transform: translateX(-105%);
  transition: transform 0.25s ease;
  z-index: 950;
  overflow-y: auto;
}

.session-drawer.open {
  transform: translateX(0);
}

.drawer-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 6px;
}

.drawer-header h3 {
  margin: 0;
}

.drawer-close {
  margin: 0;
  width: 34px;
  height: 34px;
  border-radius: 8px;
  padding: 0;
}

.drawer-subtitle {
  margin: 0 0 12px;
  color: var(--lumen-nebula-gray);
  font-size: 0.95rem;
}

.session-history {
  list-style: none;
  margin: 0;
  padding: 0;
  display: grid;
  gap: 10px;
}

.history-item,
.history-empty {
  padding: 10px 12px;
  border-radius: 10px;
  border: 1px solid color-mix(in srgb, var(--lumen-nebula-gray) 30%, transparent);
  background: color-mix(in srgb, var(--lumen-black-blue) 78%, #1b2b61 22%);
}

.history-item.correct {
  border-color: color-mix(in srgb, #49d18d 45%, transparent);
}

.history-item.incorrect {
  border-color: color-mix(in srgb, #ff5b79 45%, transparent);
}

.history-number {
  margin: 0 0 6px;
  font-size: 0.82rem;
  color: var(--lumen-nebula-gray);
  font-weight: 700;
}

.history-question {
  margin: 0 0 6px;
  line-height: 1.35;
  font-weight: 600;
}

.history-status,
.history-answer {
  margin: 0;
  font-size: 0.9rem;
}

.hero {
  margin-bottom: 20px;
  text-align: center;
  animation: fadeInUp 0.5s ease;
}

.hero-brand {
  display: flex;
  justify-content: center;
  align-items: center;
  gap: 14px;
}

.hero-logo {
  width: 56px;
  height: 56px;
  margin-bottom: 0;
  border-radius: 12px;
  filter: drop-shadow(0 0 20px color-mix(in srgb, var(--lumen-neon-cyan) 40%, transparent));
}

.tag {
  display: inline-block;
  margin: 0;
  padding: 6px 12px;
  border: 1px solid color-mix(in srgb, var(--lumen-neon-cyan) 55%, transparent);
  border-radius: 999px;
  background: color-mix(in srgb, var(--lumen-violet) 28%, transparent);
  color: var(--lumen-white);
  font-weight: 600;
}

h1 {
  margin: 10px 0 4px;
  font-size: clamp(2rem, 5vw, 3rem);
  letter-spacing: 0.5px;
}

.subtitle {
  margin: 0;
  color: var(--lumen-nebula-gray);
}

.card {
  background: color-mix(in srgb, var(--lumen-black-blue) 76%, #111a38 24%);
  backdrop-filter: blur(10px);
  border: 1px solid color-mix(in srgb, var(--lumen-nebula-gray) 45%, transparent);
  border-radius: 16px;
  padding: 20px;
  margin-bottom: 16px;
  box-shadow: 0 12px 28px color-mix(in srgb, var(--lumen-black-blue) 70%, black);
  animation: fadeInUp 0.55s ease;
}

@keyframes fadeInUp {
  from {
    opacity: 0;
    transform: translateY(12px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

h2 {
  margin-top: 0;
  margin-bottom: 12px;
}

.grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 12px;
}

label {
  display: flex;
  flex-direction: column;
  gap: 6px;
  font-weight: 600;
}

input,
select,
button {
  font: inherit;
  padding: 11px 12px;
  border-radius: 8px;
  border: 1px solid color-mix(in srgb, var(--lumen-nebula-gray) 60%, transparent);
}

input,
select {
  background: color-mix(in srgb, var(--lumen-black-blue) 76%, #162447 24%);
  color: var(--lumen-white);
}

button {
  margin-top: 12px;
  cursor: pointer;
  background: linear-gradient(90deg, color-mix(in srgb, var(--lumen-violet) 85%, white 15%), var(--lumen-neon-cyan));
  color: var(--lumen-black-blue);
  border: none;
  font-weight: 700;
  transition: transform 0.15s ease, filter 0.2s ease;
}

button:hover {
  transform: translateY(-1px);
  filter: brightness(1.08);
}

.status {
  min-height: 22px;
  margin-top: 10px;
  color: var(--lumen-nebula-gray);
  font-weight: 600;
}

.status[data-loading="true"]::after {
  content: "";
  display: inline-block;
  width: 1.2em;
  text-align: left;
  animation: dots 1.2s steps(4, end) infinite;
}

@keyframes dots {
  0% {
    content: "";
  }
  25% {
    content: ".";
  }
  50% {
    content: "..";
  }
  75% {
    content: "...";
  }
  100% {
    content: "";
  }
}

.demo-help {
  margin-top: 0;
  color: var(--lumen-nebula-gray);
}

.demo-grid {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  gap: 10px;
}

.demo-btn {
  margin-top: 0;
  text-align: left;
  min-height: 64px;
  padding: 12px;
  border-radius: 12px;
  background: linear-gradient(
    120deg,
    color-mix(in srgb, var(--lumen-violet) 55%, transparent),
    color-mix(in srgb, var(--lumen-neon-cyan) 45%, transparent)
  );
  color: var(--lumen-white);
}

.demo-btn:disabled {
  opacity: 0.65;
}

.hidden {
  display: none;
}

.question {
  margin-bottom: 18px;
  padding: 16px;
  border-radius: 12px;
  background: color-mix(in srgb, var(--lumen-black-blue) 82%, #1a2958 18%);
  border: 1px solid color-mix(in srgb, var(--lumen-nebula-gray) 30%, transparent);
  animation: fadeInUp 0.35s ease;
}

.question-head {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 6px;
}

.question-badge {
  display: inline-flex;
  padding: 4px 10px;
  border-radius: 999px;
  font-size: 0.8rem;
  font-weight: 700;
  background: color-mix(in srgb, var(--lumen-violet) 34%, transparent);
  border: 1px solid color-mix(in srgb, var(--lumen-neon-cyan) 35%, transparent);
}

.question-title {
  margin: 0 0 12px;
  line-height: 1.45;
  font-weight: 700;
  font-size: 1.15rem;
}

.options-grid {
  display: grid;
  grid-template-columns: 1fr;
  gap: 8px;
}

.option-btn {
  margin-top: 0;
  width: 100%;
  text-align: left;
  background: color-mix(in srgb, var(--lumen-black-blue) 88%, #1f2f69 12%);
  color: var(--lumen-white);
  border: 1px solid color-mix(in srgb, var(--lumen-nebula-gray) 45%, transparent);
  border-radius: 10px;
  font-weight: 600;
  padding: 13px 14px;
  transition: transform 0.15s ease, border-color 0.2s ease, box-shadow 0.2s ease;
}

.option-btn:hover {
  transform: translateY(-1px);
}

.option-btn.selected {
  border-color: color-mix(in srgb, var(--lumen-neon-cyan) 70%, transparent);
  box-shadow: 0 0 0 2px color-mix(in srgb, var(--lumen-neon-cyan) 24%, transparent);
  background: color-mix(in srgb, var(--lumen-violet) 32%, #111a40 68%);
}

.option-btn:disabled {
  opacity: 0.75;
  cursor: not-allowed;
}

.check-btn {
  margin-top: 10px;
}

.option {
  display: flex;
  align-items: center;
  gap: 8px;
  margin: 4px 0;
}

.result {
  margin-top: 10px;
  font-weight: 600;
}

.feedback {
  margin-top: 8px;
  color: var(--lumen-nebula-gray);
  line-height: 1.45;
}

.rich-content {
  line-height: 1.62;
  color: #e9efff;
  font-size: 1.05rem;
}

.rich-content h3 {
  margin: 12px 0 8px;
  font-size: 1.15rem;
  color: var(--lumen-white);
}

.rich-content strong {
  color: #ffffff;
}

.rich-content p {
  margin: 0 0 10px;
}

.rich-content .rich-list {
  margin: 0 0 12px 18px;
  padding: 0;
}

.rich-content .rich-list li {
  margin-bottom: 10px;
}

.math-inline {
  color: color-mix(in srgb, var(--lumen-neon-cyan) 75%, var(--lumen-white));
  font-weight: 600;
}

.math-block {
  margin: 8px 0;
  padding: 8px 10px;
  border-radius: 8px;
  background: color-mix(in srgb, var(--lumen-black-blue) 60%, #202f68 40%);
  border: 1px solid color-mix(in srgb, var(--lumen-neon-cyan) 35%, transparent);
  font-family: ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
  color: var(--lumen-neon-cyan);
  overflow-x: auto;
}

.rich-content .katex {
  font-size: 1.05em;
  color: #e8f7ff;
}

.rich-content .katex-display {
  margin: 10px 0;
  padding: 10px 12px;
  border-radius: 10px;
  border: 1px solid color-mix(in srgb, var(--lumen-neon-cyan) 35%, transparent);
  background: color-mix(in srgb, var(--lumen-black-blue) 58%, #1d2d66 42%);
  overflow-x: auto;
}

.math-fallback {
  display: inline-block;
  padding: 2px 8px;
  border-radius: 8px;
  border: 1px solid color-mix(in srgb, var(--lumen-neon-cyan) 35%, transparent);
  background: color-mix(in srgb, var(--lumen-black-blue) 70%, #1e2f69 30%);
  color: var(--lumen-neon-cyan);
  font-family: ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
}

@media (min-width: 900px) {
  .options-grid {
    grid-template-columns: 1fr 1fr;
  }
}

@media (max-width: 640px) {
  .grid {
    grid-template-columns: 1fr;
  }

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

  .menu-toggle {
    top: 12px;
    left: 12px;
  }

  .hero-brand {
    flex-direction: column;
    gap: 8px;
  }
}