/* ==========================================================================
   quizlet — Core Stylesheet
   Table of contents:
   1. Custom properties & reset
   2. Base typography
   3. Layout utilities
   4. Header & navigation
   5. Buttons & form controls
   6. Hero
   7. Cards (subjects, flashcards, quizzes, categories, features, resources)
   8. Stats, timeline, achievements, testimonials, FAQ
   9. Contact & newsletter
   10. Footer
   11. Flashcard demo & quiz demo widgets
   ========================================================================== */

/* ---------- 1. Custom properties & reset ---------- */
:root{
  --color-primary: #2563EB;
  --color-primary-dark: #1D4ED8;
  --color-secondary: #06B6D4;
  --color-accent: #10B981;
  --color-bg: #F8FAFC;
  --color-card: #FFFFFF;
  --color-text: #1E293B;
  --color-text-muted: #5B6B82;
  --color-border: #E2E8F0;

  --gradient-primary: linear-gradient(135deg, var(--color-primary), var(--color-secondary));
  --gradient-accent: linear-gradient(135deg, var(--color-secondary), var(--color-accent));

  --font-display: "Poppins", sans-serif;
  --font-body: "Inter", sans-serif;

  --radius-sm: 8px;
  --radius-md: 14px;
  --radius-lg: 22px;
  --radius-pill: 999px;

  --shadow-sm: 0 2px 8px rgba(30, 41, 59, 0.06);
  --shadow-md: 0 8px 24px rgba(30, 41, 59, 0.10);
  --shadow-lg: 0 20px 48px rgba(37, 99, 235, 0.16);

  --header-height: 76px;
  --container-w: 1240px;
  --transition: 220ms cubic-bezier(.4,0,.2,1);
}

[data-theme="dark"]{
  --color-bg: #0F172A;
  --color-card: #16213A;
  --color-text: #EAF0FB;
  --color-text-muted: #93A2BC;
  --color-border: #263654;
}

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

html{ scroll-behavior: smooth; }

@media (prefers-reduced-motion: reduce){
  html{ scroll-behavior: auto; }
  *, *::before, *::after{ animation-duration: 0.001ms !important; animation-iteration-count: 1 !important; transition-duration: 0.001ms !important; scroll-behavior: auto !important; }
}

body{
  font-family: var(--font-body);
  background: var(--color-bg);
  color: var(--color-text);
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
  overflow-x: hidden;
  transition: background var(--transition), color var(--transition);
}

img{ max-width: 100%; display: block; }
a{ color: inherit; text-decoration: none; }
ul{ list-style: none; }
button{ font-family: inherit; cursor: pointer; border: none; background: none; }
input, textarea, select{ font-family: inherit; }

a:focus-visible, button:focus-visible, input:focus-visible, textarea:focus-visible, [tabindex]:focus-visible{
  outline: 3px solid var(--color-secondary);
  outline-offset: 2px;
  border-radius: 4px;
}

.skip-link{
  position: absolute; left: 0; top: -60px;
  background: var(--color-primary); color: #fff; padding: 12px 20px;
  z-index: 1000; border-radius: 0 0 8px 0; transition: top var(--transition);
}
.skip-link:focus{ top: 0; }

/* ---------- 2. Base typography ---------- */
h1, h2, h3, h4{ font-family: var(--font-display); font-weight: 600; line-height: 1.2; color: var(--color-text); }
h1{ font-size: clamp(2.4rem, 4.2vw, 3.6rem); font-weight: 700; }
h2{ font-size: clamp(1.8rem, 3vw, 2.5rem); }
h3{ font-size: 1.25rem; }
p{ color: var(--color-text-muted); }

.eyebrow{
  display: inline-flex; align-items: center; gap: 8px;
  font-family: var(--font-display); font-size: 0.78rem; font-weight: 600;
  letter-spacing: 0.08em; text-transform: uppercase; color: var(--color-primary);
  background: rgba(37,99,235,0.08); padding: 6px 14px; border-radius: var(--radius-pill);
  margin-bottom: 14px;
}

.section-head{ max-width: 640px; margin: 0 auto 44px; text-align: center; }
.section-head p{ margin-top: 12px; font-size: 1.05rem; }

/* ---------- 3. Layout utilities ---------- */
.container{ max-width: var(--container-w); margin: 0 auto; padding: 0 24px; }
section{ padding: 88px 0; }
.section-alt{ background: var(--color-card); }

.grid{ display: grid; gap: 24px; }
.grid-2{ grid-template-columns: repeat(2, 1fr); }
.grid-3{ grid-template-columns: repeat(3, 1fr); }
.grid-4{ grid-template-columns: repeat(4, 1fr); }
.grid-5{ grid-template-columns: repeat(5, 1fr); }

.reveal{ opacity: 0; transform: translateY(28px); transition: opacity 700ms ease, transform 700ms ease; }
.reveal.is-visible{ opacity: 1; transform: translateY(0); }

.text-center{ text-align: center; }
.mt-40{ margin-top: 40px; }

/* ---------- 4. Header & navigation ---------- */
.site-header{
  position: sticky; top: 0; z-index: 500;
  height: var(--header-height);
  display: flex; align-items: center;
  background: rgba(248, 250, 252, 0.85);
  backdrop-filter: blur(12px);
  border-bottom: 1px solid transparent;
  transition: box-shadow var(--transition), border-color var(--transition), background var(--transition);
}
[data-theme="dark"] .site-header{ background: rgba(15, 23, 42, 0.85); }
.site-header.is-scrolled{ box-shadow: var(--shadow-sm); border-color: var(--color-border); }

.site-header .container{ display: flex; align-items: center; justify-content: space-between; gap: 24px; }

.logo{ display: flex; align-items: center; gap: 10px; font-family: var(--font-display); font-weight: 700; font-size: 1.28rem; }
.logo .logo-mark, .footer-logo .logo-mark{
  width: 38px; height: 38px; border-radius: 11px; background: var(--gradient-primary);
  display: flex; align-items: center; justify-content: center; color: #fff; flex-shrink: 0;
  transform: rotate(-6deg);
}
.logo .logo-mark svg, .footer-logo .logo-mark svg{ width: 20px; height: 20px; }
.logo span em{ font-style: normal; color: var(--color-primary); }

.main-nav{ display: flex; align-items: center; gap: 6px; }
.main-nav a{
  padding: 9px 14px; border-radius: var(--radius-pill); font-size: 0.94rem; font-weight: 500;
  color: var(--color-text-muted); transition: background var(--transition), color var(--transition);
  white-space: nowrap;
}
.main-nav a:hover, .main-nav a.active{ background: rgba(37,99,235,0.08); color: var(--color-primary); }

.header-actions{ display: flex; align-items: center; gap: 8px; }
.icon-btn{
  width: 40px; height: 40px; border-radius: 50%; display: flex; align-items: center; justify-content: center;
  color: var(--color-text); background: transparent; transition: background var(--transition);
}
.icon-btn:hover{ background: var(--color-border); }
.icon-btn svg{ width: 20px; height: 20px; }

.hamburger{ display: none; flex-direction: column; gap: 5px; width: 40px; height: 40px; align-items: center; justify-content: center; }
.hamburger span{ width: 22px; height: 2px; background: var(--color-text); border-radius: 2px; transition: transform var(--transition), opacity var(--transition); }
.hamburger.is-open span:nth-child(1){ transform: translateY(7px) rotate(45deg); }
.hamburger.is-open span:nth-child(2){ opacity: 0; }
.hamburger.is-open span:nth-child(3){ transform: translateY(-7px) rotate(-45deg); }

.search-panel{
  position: absolute; top: var(--header-height); left: 0; right: 0;
  background: var(--color-card); border-bottom: 1px solid var(--color-border);
  padding: 20px 0; box-shadow: var(--shadow-md);
  transform: translateY(-10px); opacity: 0; pointer-events: none; transition: all var(--transition);
}
.search-panel.is-open{ transform: translateY(0); opacity: 1; pointer-events: auto; }
.search-panel .container{ display: flex; gap: 12px; }
.search-panel input{
  flex: 1; padding: 13px 18px; border-radius: var(--radius-pill); border: 1px solid var(--color-border);
  background: var(--color-bg); color: var(--color-text); font-size: 0.98rem;
}
#liveSearchResults{ max-width: var(--container-w); margin: 10px auto 0; padding: 0 24px; }
.search-result-item{ padding: 10px 14px; border-radius: var(--radius-sm); display: flex; justify-content: space-between; }
.search-result-item:hover{ background: var(--color-bg); }
.search-empty{ padding: 10px 14px; color: var(--color-text-muted); font-size: 0.92rem; }

/* ---------- 5. Buttons & form controls ---------- */
.btn{
  display: inline-flex; align-items: center; justify-content: center; gap: 8px;
  padding: 13px 26px; border-radius: var(--radius-pill); font-weight: 600; font-size: 0.96rem;
  transition: transform var(--transition), box-shadow var(--transition), background var(--transition), color var(--transition);
  position: relative; overflow: hidden;
}
.btn-primary{ background: var(--gradient-primary); color: #fff; box-shadow: var(--shadow-md); }
.btn-primary:hover{ transform: translateY(-2px); box-shadow: var(--shadow-lg); }
.btn-outline{ background: transparent; color: var(--color-primary); border: 1.5px solid var(--color-border); }
.btn-outline:hover{ border-color: var(--color-primary); background: rgba(37,99,235,0.06); }
.btn-ghost{ color: var(--color-text); }
.btn-sm{ padding: 9px 18px; font-size: 0.86rem; }
.btn-block{ width: 100%; }

.ripple{ position: absolute; border-radius: 50%; transform: scale(0); animation: ripple 600ms ease-out; background: rgba(255,255,255,0.55); pointer-events: none; }
@keyframes ripple{ to{ transform: scale(3); opacity: 0; } }

.field{ margin-bottom: 18px; }
.field label{ display: block; font-size: 0.88rem; font-weight: 600; margin-bottom: 7px; }
.field input, .field textarea, .field select{
  width: 100%; padding: 12px 16px; border-radius: var(--radius-sm); border: 1px solid var(--color-border);
  background: var(--color-bg); color: var(--color-text); font-size: 0.96rem; transition: border-color var(--transition);
}
.field input:focus, .field textarea:focus, .field select:focus{ border-color: var(--color-primary); }

/* ---------- 6. Hero ---------- */
.hero{
  position: relative; padding: 64px 0 100px; overflow: hidden;
  background: linear-gradient(180deg, #EEF3FF 0%, var(--color-bg) 78%);
}
[data-theme="dark"] .hero{ background: linear-gradient(180deg, #142042 0%, var(--color-bg) 78%); }
.hero .container{ display: grid; grid-template-columns: 1.05fr 0.95fr; gap: 48px; align-items: center; }

.hero-shapes span{
  position: absolute; border-radius: 40%; filter: blur(2px); opacity: 0.5;
  animation: float 7s ease-in-out infinite;
}
.hero-shapes span:nth-child(1){ width: 90px; height: 90px; top: 8%; left: 4%; background: var(--gradient-primary); animation-delay: 0s; }
.hero-shapes span:nth-child(2){ width: 60px; height: 60px; top: 66%; left: 10%; background: var(--color-accent); border-radius: 50%; animation-delay: 1.2s; }
.hero-shapes span:nth-child(3){ width: 120px; height: 120px; top: 20%; right: 6%; background: var(--gradient-accent); border-radius: 30%; animation-delay: 2s; }
.hero-shapes span:nth-child(4){ width: 50px; height: 50px; bottom: 10%; right: 14%; background: var(--color-secondary); border-radius: 50%; animation-delay: 0.6s; }
@keyframes float{ 0%,100%{ transform: translateY(0) rotate(0deg);} 50%{ transform: translateY(-22px) rotate(8deg);} }

.hero-text .eyebrow{ margin-bottom: 18px; }
.hero-text h1{ margin-bottom: 18px; }
.hero-text h1 .highlight{ background: var(--gradient-primary); -webkit-background-clip: text; background-clip: text; color: transparent; }
.hero-text > p{ font-size: 1.12rem; max-width: 520px; margin-bottom: 30px; }

.hero-search{ display: flex; gap: 10px; max-width: 480px; margin-bottom: 22px; }
.hero-search input{
  flex: 1; padding: 15px 20px; border-radius: var(--radius-pill); border: 1px solid var(--color-border);
  background: var(--color-card); box-shadow: var(--shadow-sm); font-size: 0.98rem; color: var(--color-text);
}
.hero-cta{ display: flex; gap: 14px; flex-wrap: wrap; }

.hero-visual{ position: relative; display: flex; align-items: center; justify-content: center; min-height: 380px; }
.floating-stack{ position: relative; width: 320px; height: 340px; }
.float-card{
  position: absolute; width: 250px; background: var(--color-card); border-radius: var(--radius-md);
  box-shadow: var(--shadow-lg); padding: 20px; border: 1px solid var(--color-border);
  animation: floatCard 6s ease-in-out infinite;
}
.float-card.card-1{ top: 0; left: 0; z-index: 3; animation-delay: 0s; }
.float-card.card-2{ top: 70px; left: 55px; z-index: 2; opacity: 0.9; animation-delay: 1s; }
.float-card.card-3{ top: 140px; left: 8px; z-index: 1; opacity: 0.75; animation-delay: 2s; }
@keyframes floatCard{ 0%,100%{ transform: translateY(0);} 50%{ transform: translateY(-14px);} }
.float-card .tag{ display: inline-block; font-size: 0.72rem; font-weight: 700; color: var(--color-primary); background: rgba(37,99,235,0.1); padding: 4px 10px; border-radius: var(--radius-pill); margin-bottom: 10px; }
.float-card h4{ font-size: 1rem; margin-bottom: 6px; }
.float-card p{ font-size: 0.82rem; margin: 0; }

/* ---------- 7. Cards ---------- */
.subject-card, .category-card, .feature-card, .resource-card, .why-card, .tip-card{
  background: var(--color-card); border: 1px solid var(--color-border); border-radius: var(--radius-md);
  padding: 26px; transition: transform var(--transition), box-shadow var(--transition), border-color var(--transition);
}
.subject-card:hover, .category-card:hover, .feature-card:hover, .resource-card:hover, .why-card:hover, .tip-card:hover{
  transform: translateY(-6px); box-shadow: var(--shadow-md); border-color: rgba(37,99,235,0.25);
}
.card-icon{
  width: 52px; height: 52px; border-radius: var(--radius-sm); display: flex; align-items: center; justify-content: center;
  background: var(--gradient-primary); color: #fff; margin-bottom: 16px;
}
.card-icon svg{ width: 26px; height: 26px; }
.subject-card h3{ margin-bottom: 4px; }
.subject-card .set-count{ font-size: 0.85rem; color: var(--color-text-muted); }

.flashcard-set, .quiz-card{
  background: var(--color-card); border: 1px solid var(--color-border); border-radius: var(--radius-md);
  padding: 24px; display: flex; flex-direction: column; gap: 12px; transition: transform var(--transition), box-shadow var(--transition);
}
.flashcard-set:hover, .quiz-card:hover{ transform: translateY(-6px); box-shadow: var(--shadow-md); }
.set-meta{ display: flex; align-items: center; gap: 10px; font-size: 0.8rem; color: var(--color-text-muted); flex-wrap: wrap; }
.badge{ padding: 3px 10px; border-radius: var(--radius-pill); font-size: 0.72rem; font-weight: 700; }
.badge-easy{ background: rgba(16,185,129,0.12); color: var(--color-accent); }
.badge-medium{ background: rgba(37,99,235,0.12); color: var(--color-primary); }
.badge-hard{ background: rgba(239,68,68,0.12); color: #EF4444; }
.set-actions{ display: flex; gap: 8px; align-items: center; margin-top: auto; }
.fav-btn{ width: 38px; height: 38px; border-radius: 50%; border: 1px solid var(--color-border); display: flex; align-items: center; justify-content: center; transition: all var(--transition); }
.fav-btn svg{ width: 17px; height: 17px; stroke: var(--color-text-muted); fill: none; transition: all var(--transition); }
.fav-btn.is-active svg{ fill: #EF4444; stroke: #EF4444; }

/* ---------- 8. Stats, timeline, achievements, testimonials, FAQ ---------- */
.stats-section{ background: var(--gradient-primary); color: #fff; padding: 56px 0; }
.stats-section h2, .stats-section p{ color: #fff; }
.stats-grid{ grid-template-columns: repeat(4, 1fr); text-align: center; }
.stat-number{ font-family: var(--font-display); font-size: clamp(2.1rem, 4vw, 3rem); font-weight: 700; }
.stat-label{ opacity: 0.9; font-size: 0.92rem; margin-top: 4px; }

.timeline{ position: relative; display: flex; justify-content: space-between; gap: 12px; flex-wrap: wrap; }
.timeline::before{ content: ""; position: absolute; top: 26px; left: 6%; right: 6%; height: 2px; background: var(--color-border); z-index: 0; }
.timeline-step{ position: relative; z-index: 1; flex: 1; min-width: 140px; text-align: center; }
.timeline-step .step-dot{
  width: 52px; height: 52px; border-radius: 50%; background: var(--color-card); border: 2px solid var(--color-primary);
  display: flex; align-items: center; justify-content: center; margin: 0 auto 14px; font-family: var(--font-display); font-weight: 700; color: var(--color-primary);
}
.timeline-step h4{ font-size: 0.98rem; margin-bottom: 4px; }
.timeline-step p{ font-size: 0.82rem; }

.achievement-badge{ text-align: center; padding: 22px; background: var(--color-card); border: 1px solid var(--color-border); border-radius: var(--radius-md); }
.badge-icon{ width: 60px; height: 60px; border-radius: 50%; background: var(--gradient-accent); display: flex; align-items: center; justify-content: center; margin: 0 auto 14px; color: #fff; }
.badge-icon svg{ width: 28px; height: 28px; }

.testimonial-track{ display: grid; grid-template-columns: repeat(2, 1fr); gap: 24px; align-items: stretch; }
.testimonial-slide{ display: flex; justify-content: center; }
.testimonial-card{
  position: relative; width: 100%; max-width: 620px; background: var(--color-card); border: 1px solid var(--color-border); border-radius: var(--radius-lg);
  padding: 32px 32px 28px; text-align: left; box-shadow: var(--shadow-sm); transition: transform var(--transition), box-shadow var(--transition);
}
.testimonial-card:hover{ transform: translateY(-4px); box-shadow: var(--shadow-md); }
.testimonial-card::before{
  content: "\201C"; position: absolute; top: 14px; right: 22px; font-family: var(--font-display); font-size: 3.2rem; line-height: 1;
  color: var(--color-primary); opacity: 0.15; font-style: normal;
}
.testimonial-card-head{ display: flex; align-items: center; gap: 14px; margin-bottom: 14px; }
.testimonial-avatar{ width: 52px; height: 52px; border-radius: 50%; background: var(--gradient-primary); color:#fff; display:flex; align-items:center; justify-content:center; font-family: var(--font-display); font-weight: 700; flex-shrink: 0; box-shadow: 0 0 0 3px var(--color-bg), 0 0 0 4px var(--color-border); }
.testimonial-name h4{ font-size: 0.98rem; margin: 0; }
.testimonial-name p{ font-size: 0.82rem; margin: 2px 0 0; color: var(--color-text-muted); }
.stars{ color: #F59E0B; letter-spacing: 2px; margin-bottom: 10px; font-size: 0.92rem; }
.testimonial-card p.testimonial-text{ font-size: 0.96rem; line-height: 1.65; color: var(--color-text); }
.testimonial-controls{ display: flex; justify-content: center; gap: 16px; margin-top: 22px; }
.dot-nav{ display: flex; gap: 8px; align-items: center; justify-content: center; margin-top: 16px; }
.dot-nav button{ width: 8px; height: 8px; border-radius: 50%; background: var(--color-border); transition: all var(--transition); }
.dot-nav button.is-active{ width: 22px; border-radius: var(--radius-pill); background: var(--color-primary); }

.faq-grid{ grid-template-columns: 1fr 1fr; align-items: start; }
.faq-item{ border: 1px solid var(--color-border); border-radius: var(--radius-sm); margin-bottom: 12px; background: var(--color-card); overflow: hidden; }
.faq-question{ width: 100%; display: flex; justify-content: space-between; align-items: center; padding: 16px 20px; text-align: left; font-weight: 600; font-family: var(--font-display); font-size: 0.96rem; }
.faq-question svg{ width: 18px; height: 18px; flex-shrink: 0; transition: transform var(--transition); }
.faq-item.is-open .faq-question svg{ transform: rotate(45deg); }
.faq-answer{ max-height: 0; overflow: hidden; transition: max-height var(--transition); }
.faq-answer p{ padding: 0 20px 18px; font-size: 0.92rem; }

/* ---------- 9. Contact & newsletter ---------- */
.contact-grid{ grid-template-columns: 1fr 1fr; align-items: start; gap: 40px; }
.contact-form-card{ background: var(--color-card); border: 1px solid var(--color-border); border-radius: var(--radius-lg); padding: 32px; box-shadow: var(--shadow-sm); }
.contact-card{ display: flex; gap: 12px; padding: 14px; border: 1px solid var(--color-border); border-radius: var(--radius-sm); margin-bottom: 10px; background: var(--color-card); }
.contact-card .card-icon{ margin-bottom: 0; width: 36px; height: 36px; flex-shrink: 0; }
.contact-card h3{ font-size: 0.98rem; margin-bottom: 2px; }
.contact-card p{ font-size: 0.86rem; margin: 0; }
.social-icons{ display: flex; gap: 10px; margin-top: 16px; }

.newsletter-section{ background: var(--gradient-accent); border-radius: var(--radius-lg); padding: 48px; text-align: center; color: #fff; }
.newsletter-section h2, .newsletter-section p{ color: #fff; }
.newsletter-form{ display: flex; gap: 10px; max-width: 440px; margin: 22px auto 0; }
.newsletter-form input{ flex: 1; padding: 13px 18px; border-radius: var(--radius-pill); border: none; }
.newsletter-msg{ margin-top: 14px; font-size: 0.9rem; font-weight: 600; }

/* ---------- 10. Footer ---------- */
.site-footer{ background: #101B33; color: #C6D2E8; padding: 72px 0 0; }
[data-theme="dark"] .site-footer{ background: #060B18; }
.footer-grid{ grid-template-columns: 1.4fr 1fr 1fr 1fr; padding-bottom: 48px; border-bottom: 1px solid rgba(255,255,255,0.08); }
.footer-grid h4{ color: #fff; font-size: 0.95rem; margin-bottom: 16px; }
.footer-grid li{ margin-bottom: 10px; }
.footer-grid a{ color: #9FB0CC; font-size: 0.92rem; transition: color var(--transition); }
.footer-grid a:hover{ color: #fff; }
.footer-logo{ color: #fff; font-family: var(--font-display); font-weight: 700; font-size: 1.2rem; margin-bottom: 12px; display: flex; align-items: center; gap: 10px; text-decoration: none; width: fit-content; transition: opacity var(--transition); }
.footer-logo:hover{ opacity: 0.85; }
.footer-about p{ color: #93A2BC; font-size: 0.92rem; max-width: 320px; }
.footer-bottom{ display: flex; justify-content: space-between; align-items: center; padding: 24px 0; flex-wrap: wrap; gap: 12px; font-size: 0.85rem; }
.footer-social{ display: flex; gap: 10px; }
.footer-social a{ width: 36px; height: 36px; border-radius: 50%; background: rgba(255,255,255,0.06); display: flex; align-items: center; justify-content: center; transition: background var(--transition); }
.footer-social a:hover{ background: var(--color-primary); }
.footer-social svg{ width: 16px; height: 16px; }

.back-to-top{
  position: fixed; right: 26px; bottom: 26px; width: 46px; height: 46px; border-radius: 50%;
  background: var(--gradient-primary); color: #fff; display: flex; align-items: center; justify-content: center;
  box-shadow: var(--shadow-md); opacity: 0; pointer-events: none; transform: translateY(12px);
  transition: all var(--transition); z-index: 400;
}
.back-to-top.is-visible{ opacity: 1; pointer-events: auto; transform: translateY(0); }

/* ---------- 11. Flashcard demo & quiz demo widgets ---------- */
.flashcard-demo{ display: flex; flex-direction: column; align-items: center; gap: 22px; }
.flip-scene{ width: min(480px, 90vw); height: 280px; perspective: 1400px; }
.flip-card{ position: relative; width: 100%; height: 100%; transition: transform 600ms; transform-style: preserve-3d; cursor: pointer; }
.flip-card.is-flipped{ transform: rotateY(180deg); }
.flip-face{
  position: absolute; inset: 0; backface-visibility: hidden; border-radius: var(--radius-lg);
  display: flex; flex-direction: column; align-items: center; justify-content: center; text-align: center; padding: 30px;
  box-shadow: var(--shadow-lg); border: 1px solid var(--color-border);
}
.flip-front{ background: var(--color-card); }
.flip-back{ background: var(--gradient-primary); color: #fff; transform: rotateY(180deg); }
.flip-face .flip-label{ font-size: 0.75rem; text-transform: uppercase; letter-spacing: 0.1em; font-weight: 700; opacity: 0.7; margin-bottom: 14px; }
.flip-face h3{ font-size: 1.5rem; color: inherit; }
.flip-progress{ font-size: 0.85rem; color: var(--color-text-muted); }
.flashcard-controls{ display: flex; gap: 10px; align-items: center; flex-wrap: wrap; justify-content: center; }
.flashcard-controls .icon-btn{ border: 1px solid var(--color-border); }

.quiz-demo{ max-width: 620px; margin: 0 auto; background: var(--color-card); border: 1px solid var(--color-border); border-radius: var(--radius-lg); padding: 32px; }
.quiz-progress-bar{ height: 8px; border-radius: var(--radius-pill); background: var(--color-border); overflow: hidden; margin-bottom: 22px; }
.quiz-progress-fill{ height: 100%; background: var(--gradient-primary); width: 0%; transition: width var(--transition); }
.quiz-option{ display: block; width: 100%; text-align: left; padding: 14px 18px; border: 1.5px solid var(--color-border); border-radius: var(--radius-sm); margin-bottom: 10px; transition: all var(--transition); }
.quiz-option:hover{ border-color: var(--color-primary); }
.quiz-option.is-correct{ border-color: var(--color-accent); background: rgba(16,185,129,0.08); }
.quiz-option.is-wrong{ border-color: #EF4444; background: rgba(239,68,68,0.08); }
.quiz-result{ text-align: center; }
.quiz-result .score{ font-family: var(--font-display); font-size: 3rem; font-weight: 700; color: var(--color-primary); }

.progress-track{ display: grid; grid-template-columns: repeat(4, 1fr); gap: 20px; }
.progress-stat{ background: var(--color-card); border: 1px solid var(--color-border); border-radius: var(--radius-md); padding: 22px; }
.progress-bar-row{ height: 10px; border-radius: var(--radius-pill); background: var(--color-border); overflow: hidden; margin-top: 10px; }
.progress-bar-fill{ height: 100%; background: var(--gradient-accent); }

.filter-bar{ display: flex; gap: 10px; flex-wrap: wrap; margin-bottom: 30px; }
.filter-chip{ padding: 9px 18px; border-radius: var(--radius-pill); border: 1.5px solid var(--color-border); font-size: 0.88rem; font-weight: 500; transition: all var(--transition); }
.filter-chip.is-active{ background: var(--color-primary); color: #fff; border-color: var(--color-primary); }

.loading-spinner{ width: 22px; height: 22px; border: 3px solid var(--color-border); border-top-color: var(--color-primary); border-radius: 50%; animation: spin 800ms linear infinite; }
@keyframes spin{ to{ transform: rotate(360deg); } }

.page-hero{ padding: 70px 0 40px; text-align: center; background: linear-gradient(180deg, #EEF3FF 0%, var(--color-bg) 100%); }
[data-theme="dark"] .page-hero{ background: linear-gradient(180deg, #142042 0%, var(--color-bg) 100%); }
.breadcrumbs{ font-size: 0.85rem; color: var(--color-text-muted); margin-bottom: 14px; }
.breadcrumbs a{ color: var(--color-primary); }

.legal-content h2{ margin: 30px 0 12px; font-size: 1.3rem; }
.legal-content p, .legal-content li{ margin-bottom: 12px; }
.legal-content ul{ padding-left: 20px; list-style: disc; }
.updated-note{ color: var(--color-text-muted); font-size: 0.88rem; margin-bottom: 30px; }

.empty-state{ text-align: center; padding: 60px 20px; color: var(--color-text-muted); }
.empty-state svg{ width: 54px; height: 54px; margin-bottom: 16px; opacity: 0.6; }

/* ---------- Study session modal ---------- */
.study-modal-overlay{
  position: fixed; inset: 0; background: rgba(15, 23, 42, 0.6); backdrop-filter: blur(3px);
  display: flex; align-items: center; justify-content: center; padding: 24px;
  opacity: 0; pointer-events: none; transition: opacity var(--transition); z-index: 900;
}
.study-modal-overlay.is-open{ opacity: 1; pointer-events: auto; }
.study-modal{
  width: min(560px, 100%); max-height: 90vh; overflow-y: auto; background: var(--color-bg);
  border-radius: var(--radius-lg); padding: 28px; box-shadow: var(--shadow-lg);
  transform: translateY(16px); transition: transform var(--transition);
}
.study-modal-overlay.is-open .study-modal{ transform: translateY(0); }
.study-modal-head{ display: flex; justify-content: space-between; align-items: flex-start; margin-bottom: 18px; gap: 12px; }
.study-modal-eyebrow{ font-size: 0.78rem; font-weight: 700; text-transform: uppercase; letter-spacing: 0.06em; color: var(--color-primary); margin-bottom: 4px; }
.study-modal [data-modal-finish]{ margin-top: 18px; }