/* =========================================================
   WARM DESIGN SYSTEM — Design Tokens
   ========================================================= */
:root {
  --color-black:       rgba(0,0,0,0.95);
  --color-black-solid: #000000;
  --color-white:       #ffffff;
  --color-accent:        #0075de;
  --color-accent-active: #005bab;
  --color-accent-focus:  #097fe8;

  --warm-white:    #f6f5f4;
  --warm-dark:     #31302e;
  --warm-gray-500: #615d59;
  --warm-gray-300: #a39e98;

  --color-teal:   #2a9d99;
  --color-green:  #1aae39;
  --color-orange: #dd5b00;

  --badge-bg:   #f2f9ff;
  --badge-text: #097fe8;

  --app-error-banner-bg: rgba (221, 91, 0, 0.08);
  --app-error-banner-border: rgba(221, 91, 0, 0.25);

  /* Semantic aliases — Light Mode */
  --bg-page:    var(--color-white);
  --bg-surface: var(--color-white);
  --bg-warm:    var(--warm-white);
  --text-primary:   var(--color-black);
  --text-secondary: var(--warm-gray-500);
  --text-muted:     var(--warm-gray-300);
  --text-inverse:   var(--color-white);
  --text-link:      var(--color-accent);
  --border-whisper: 1px solid rgba(0,0,0,0.1);
  --border-medium:  1px solid rgba(0,0,0,0.18);
  --border-color:   rgba(0,0,0,0.1);
  --border-focus:   var(--color-accent-focus);

  /* Typography */
  --font-sans: 'Inter', -apple-system, system-ui, 'Segoe UI', Helvetica, Arial, sans-serif;
  --font-mono: 'Roboto Mono', 'Consolas', 'Menlo', monospace;

  /* Font sizes */
  --text-display: 3rem;
  --text-h2:      2rem;
  --text-h3:      1.5rem;
  --text-h4:      1.25rem;
  --text-body-lg: 1.125rem;
  --text-body:    1rem;
  --text-caption: 0.875rem;
  --text-badge:   0.75rem;

  /* Font weights */
  --fw-regular:  400;
  --fw-medium:   500;
  --fw-semibold: 600;
  --fw-bold:     700;

  /* Line heights */
  --lh-display: 1.05;
  --lh-h2:      1.25;
  --lh-body:    1.55;

  /* Letter spacing */
  --ls-display: -1.5px;
  --ls-h2:      -0.75px;
  --ls-h4:      -0.25px;
  --ls-badge:   0.125px;

  /* Spacing — 8px grid */
  --space-1: 0.25rem;
  --space-2: 0.5rem;
  --space-3: 0.75rem;
  --space-4: 1rem;
  --space-5: 1.5rem;
  --space-6: 2rem;
  --space-7: 3rem;
  --space-8: 4rem;

  /* Border radius */
  --radius-micro:  4px;
  --radius-subtle: 5px;
  --radius-sm:     8px;
  --radius-md:     12px;
  --radius-lg:     16px;
  --radius-pill:   9999px;

  /* Shadows */
  --shadow-card:
    rgba(0,0,0,0.040) 0px 4px 18px 0px,
    rgba(0,0,0,0.027) 0px 2px 7px 0px,
    rgba(0,0,0,0.010) 0px 0.175px 1.04px 0px;
  --shadow-deep:
    rgba(0,0,0,0.010) 0px 1px 3px 0px,
    rgba(0,0,0,0.020) 0px 3px 7px 0px,
    rgba(0,0,0,0.030) 0px 7px 15px 0px,
    rgba(0,0,0,0.040) 0px 14px 28px 0px;
  --shadow-focus:
    0 0 0 2px var(--color-white),
    0 0 0 4px var(--color-accent-focus);

  /* Transitions */
  --dur-fast:   100ms;
  --dur-base:   150ms;
  --dur-slow:   250ms;
  --ease:       cubic-bezier(0.4, 0, 0.2, 1);
  --ease-out:   cubic-bezier(0, 0, 0.2, 1);
  --ease-spring:cubic-bezier(0.34, 1.56, 0.64, 1);
}

/* =========================================================
   DARK MODE
   ========================================================= */
[data-theme="dark"] {
  --bg-page:    #191919;
  --bg-surface: #202020;
  --bg-warm:    #252525;
  --text-primary:   rgba(255,255,255,0.92);
  --text-secondary: #9b9a97;
  --text-muted:     #6b6b69;
  --text-inverse:   #000000;
  --text-link:      #4d9de0;
  --border-color:   rgba(255,255,255,0.09);
  --border-whisper: 1px solid rgba(255,255,255,0.09);
  --border-medium:  1px solid rgba(255,255,255,0.15);
  --border-focus:   var(--color-accent);
  --color-accent:        #4d9de0;
  --color-accent-active: #3a7fc1;
  --badge-bg:   rgba(77,157,224,0.12);
  --badge-text: #4d9de0;
  --warm-gray-500: #9b9a97;
  --warm-gray-300: #6b6b69;
  --shadow-card:
    rgba(0,0,0,0.25) 0px 4px 18px 0px,
    rgba(0,0,0,0.20) 0px 2px 7px 0px;
  --shadow-deep:
    rgba(0,0,0,0.30) 0px 1px 3px 0px,
    rgba(0,0,0,0.35) 0px 7px 15px 0px,
    rgba(0,0,0,0.40) 0px 23px 52px 0px;
  --shadow-focus:
    0 0 0 2px var(--bg-surface),
    0 0 0 4px var(--color-accent);
}

@media (prefers-color-scheme: dark) {
  html:not([data-theme="light"]) {
    --bg-page:    #191919;
    --bg-surface: #202020;
    --bg-warm:    #252525;
    --text-primary:   rgba(255,255,255,0.92);
    --text-secondary: #9b9a97;
    --text-muted:     #6b6b69;
    --text-link:      #4d9de0;
    --border-color:   rgba(255,255,255,0.09);
    --border-whisper: 1px solid rgba(255,255,255,0.09);
    --border-medium:  1px solid rgba(255,255,255,0.15);
    --color-accent:    #4d9de0;
    --badge-bg:  rgba(77,157,224,0.12);
    --badge-text:#4d9de0;
    --warm-gray-500: #9b9a97;
    --warm-gray-300: #6b6b69;
    --shadow-card:
      rgba(0,0,0,0.25) 0px 4px 18px 0px,
      rgba(0,0,0,0.20) 0px 2px 7px 0px;
    --shadow-deep:
      rgba(0,0,0,0.35) 0px 7px 15px 0px,
      rgba(0,0,0,0.40) 0px 23px 52px 0px;
  }
}

/* =========================================================
   GLOBAL RESET & BASE
   ========================================================= */
*, *::before, *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}
html { scroll-behavior: smooth; }
body {
  font-family: var(--font-sans);
  font-size: 16px;
  font-weight: var(--fw-regular);
  line-height: var(--lh-body);
  color: var(--text-primary);
  background: var(--bg-page);
  -webkit-font-smoothing: antialiased;
  transition: background var(--dur-slow) var(--ease), color var(--dur-slow) var(--ease);
}

/* =========================================================
   LAYOUT
   ========================================================= */
.container {
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 var(--space-6);
}

/* =========================================================
   NAVBAR
   ========================================================= */
.app-nav {
  position: sticky;
  top: 0;
  z-index: 200;
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 12px 32px;
  background: color-mix(in srgb, var(--bg-page) 92%, transparent);
  backdrop-filter: blur(12px);
  border-bottom: var(--border-whisper);
  transition: background var(--dur-slow) var(--ease);
}
.nav-brand {
  display: flex;
  align-items: center;
  gap: 10px;
  font-size: 15px;
  font-weight: var(--fw-bold);
  color: var(--text-primary);
  letter-spacing: -0.3px;
}
.nav-logo {
  width: 24px;
  height: 24px;
  /* background: var( --color-accent); */
  border-radius: var(--radius-micro);
  display: flex;
  align-items: center;
  justify-content: center;
  color: var( --color-accent);
  font-size: 13px;
  font-weight: var(--fw-bold);
  flex-shrink: 0;
}
[data-theme="dark"] .nav-logo {
  /* background: var(--text-primary); */
  color: var(var( --color-accent));
}
.nav-actions {
  display: flex;
  align-items: center;
  gap: 8px;
}

/* Theme Toggle */
.theme-toggle {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 32px;
  height: 32px;
  border-radius: var(--radius-micro);
  border: var(--border-whisper);
  background: transparent;
  color: var(--text-secondary);
  cursor: pointer;
  transition: background var(--dur-base) var(--ease), color var(--dur-base) var(--ease);
}
.theme-toggle:hover {
  background: var(--bg-warm);
  color: var(--text-primary);
}
.icon-sun  { display: none; }
.icon-moon { display: block; }
[data-theme="dark"] .icon-sun  { display: block; }
[data-theme="dark"] .icon-moon { display: none; }

/* =========================================================
   HERO SECTION
   ========================================================= */
.hero-section {
  background: var(--bg-warm);
  border-bottom: var(--border-whisper);
  padding: var(--space-8) 0 var(--space-7);
}
.hero-eyebrow {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 4px 12px;
  background: var(--badge-bg);
  color: var(--badge-text);
  border-radius: var(--radius-pill);
  font-size: var(--text-badge);
  font-weight: var(--fw-semibold);
  letter-spacing: var(--ls-badge);
  text-transform: uppercase;
  margin-bottom: var(--space-5);
}
.hero-title {
  font-size: var(--text-display);
  font-weight: var(--fw-bold);
  line-height: var(--lh-display);
  letter-spacing: var(--ls-display);
  color: var(--text-primary);
  margin-bottom: var(--space-4);
}
.hero-desc {
  font-size: var(--text-body-lg);
  color: var(--text-secondary);
  line-height: 1.6;
  max-width: 520px;
}

/* =========================================================
   MAIN CONTENT
   ========================================================= */
.main-content {
  padding: var(--space-7) 0 var(--space-8);
}
.main-layout {
  display: grid;
  grid-template-columns: 280px 1fr;
  gap: var(--space-7);
  align-items: start;
}

/* =========================================================
   FILTER SIDEBAR
   ========================================================= */
.filter-sidebar {
  position: sticky;
  top: 72px;
}
.filter-sidebar-header {
  margin-bottom: var(--space-5);
}
.filter-sidebar-title {
  font-size: var(--text-h4);
  font-weight: var(--fw-bold);
  letter-spacing: var(--ls-h4);
  color: var(--text-primary);
  margin-bottom: 4px;
}
.filter-sidebar-subtitle {
  font-size: var(--text-caption);
  color: var(--text-muted);
}

/* Filter Panel (accordion-style) */
.filter-panel {
  background: var(--bg-surface);
  border: var(--border-whisper);
  border-radius: var(--radius-md);
  box-shadow: var(--shadow-card);
  overflow: hidden;
  margin-bottom: var(--space-4);
}

.filter-panel-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 12px 16px;
  cursor: pointer;
  user-select: none;
  border-bottom: var(--border-whisper);
  transition: background var(--dur-base) var(--ease);
  background: var(--bg-warm);
}
.filter-panel-header:hover {
  background: color-mix(in srgb, var(--bg-warm) 85%, var(--bg-surface));
}
.filter-panel-label {
  font-size: var(--text-caption);
  font-weight: var(--fw-semibold);
  color: var(--text-primary);
  letter-spacing: 0.1px;
}
.filter-panel-chevron {
  width: 16px;
  height: 16px;
  color: var(--text-muted);
  transition: transform var(--dur-base) var(--ease);
  flex-shrink: 0;
}
.filter-panel.is-open .filter-panel-chevron {
  transform: rotate(180deg);
}

.filter-panel-body {
  display: none;
  padding: var(--space-4);
  border-top: var(--border-whisper);
}
.filter-panel.is-open .filter-panel-body {
  display: block;
}

/* Checkbox grid inside panel */
.checkbox-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 6px;
  margin-bottom: var(--space-4);
}
.checkbox-grid-single {
  grid-template-columns: 1fr;
}

/* .form-check */
.form-check {
  display: flex;
  align-items: flex-start;
  gap: 8px;
  cursor: pointer;
  padding: 3px 0;
}
.form-check input[type="checkbox"] {
  appearance: none;
  width: 15px;
  height: 15px;
  border: var(--border-medium);
  border-radius: 3px;
  background: var(--bg-surface);
  cursor: pointer;
  flex-shrink: 0;
  position: relative;
  transition: all var(--dur-base) var(--ease);
}
.form-check input[type="checkbox"]:hover {
  border-color: var(--color-accent);
}
.form-check input[type="checkbox"]:checked {
  background: var(--color-accent);
  border-color: var(--color-accent);
}
.form-check input[type="checkbox"]:checked::after {
  content: '';
  position: absolute;
  top: 2px;
  left: 4px;
  width: 5px;
  height: 8px;
  border: 2px solid white;
  border-top: none;
  border-left: none;
  transform: rotate(45deg);
}
.form-check input[type="checkbox"]:focus {
  outline: none;
  box-shadow: var(--shadow-focus);
}
.form-check-label {
  font-size: var(--text-caption);
  color: var(--text-primary);
  line-height: 1.3;
}

/* Panel select/deselect actions */
.filter-panel-actions {
  display: flex;
  gap: var(--space-2);
  padding-top: var(--space-3);
  border-top: var(--border-whisper);
}

/* =========================================================
   GENERATOR CONTROLS
   ========================================================= */
.controls-section {
  margin-bottom: var(--space-7);
}

.controls-row {
  display: flex;
  align-items: flex-end;
  gap: var(--space-4);
  flex-wrap: wrap;
}

.form-group {
  display: flex;
  flex-direction: column;
  gap: 6px;
}
.form-label {
  font-size: var(--text-caption);
  font-weight: var(--fw-medium);
  color: var(--text-primary);
}

.form-input {
  height: 38px;
  padding: 0 12px;
  background: var(--bg-surface);
  border: var(--border-whisper);
  border-radius: var(--radius-micro);
  font-family: var(--font-sans);
  font-size: var(--text-body);
  color: var(--text-primary);
  outline: none;
  width: 100px;
  transition: border-color var(--dur-base) var(--ease), box-shadow var(--dur-base) var(--ease);
}
.form-input::placeholder { color: var(--text-muted); }
.form-input:hover  { border-color: rgba(0,0,0,0.25); }
.form-input:focus  { border-color: var(--color-accent); box-shadow: var(--shadow-focus); }
[data-theme="dark"] .form-input:hover { border-color: rgba(255,255,255,0.22); }

.action-buttons {
  display: flex;
  gap: var(--space-2);
  flex-wrap: wrap;
}

/* =========================================================
   BUTTONS
   ========================================================= */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 6px;
  height: 38px;
  padding: 0 18px;
  border-radius: var(--radius-subtle);
  border: var(--border-whisper);
  font-family: var(--font-sans);
  font-size: var(--text-caption);
  font-weight: var(--fw-medium);
  cursor: pointer;
  text-decoration: none;
  white-space: nowrap;
  transition:
    background var(--dur-base) var(--ease),
    border-color var(--dur-base) var(--ease),
    box-shadow var(--dur-base) var(--ease),
    transform var(--dur-fast) var(--ease);
}
.btn:focus-visible {
  outline: none;
  box-shadow: var(--shadow-focus);
}
.btn:active {
  transform: scale(0.97);
}

.btn-blue {
  background: var(--color-accent);
  color: #fff;
  border-color: transparent;
}
.btn-blue:hover { background: var(--color-accent-active); }

.btn-secondary {
  background: rgba(0,0,0,0.06);
  color: var(--text-primary);
  border-color: transparent;
}
.btn-secondary:hover { background: rgba(0,0,0,0.10); }
[data-theme="dark"] .btn-secondary { background: rgba(255,255,255,0.08); }
[data-theme="dark"] .btn-secondary:hover { background: rgba(255,255,255,0.13); }

.btn-ghost {
  background: transparent;
  color: var(--text-secondary);
  border-color: transparent;
  font-size: var(--text-badge);
  height: 30px;
  padding: 0 10px;
}
.btn-ghost:hover {
  background: var(--bg-warm);
  color: var(--text-primary);
}

.btn-danger {
  background: rgba(239,68,68,0.9);
  color: #fff;
  border-color: transparent;
}
.btn-danger:hover { background: rgb(220,38,38); }

/* =========================================================
   RESULTS SECTION
   ========================================================= */
.results-section {}

.results-header {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  margin-bottom: var(--space-5);
  padding-bottom: var(--space-4);
  border-bottom: var(--border-whisper);
}

.results-title {
  font-size: var(--text-h3);
  font-weight: var(--fw-bold);
  letter-spacing: -0.5px;
  color: var(--text-primary);
}

.results-count {
  font-size: var(--text-badge);
  font-weight: var(--fw-semibold);
  color: var(--text-muted);
  font-family: var(--font-mono);
}

.results-empty {
  text-align: center;
  padding: var(--space-8) var(--space-5);
  color: var(--text-muted);
}
.results-empty-icon {
  font-size: 2.5rem;
  margin-bottom: var(--space-4);
  display: block;
  opacity: 0.5;
}
.results-empty-text {
  font-size: var(--text-body);
  color: var(--text-muted);
}

/* Book card grid */
#container-generated-books {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: var(--space-5);
}

/* ds-card: book result card */
.ds-card {
  background: var(--bg-surface);
  border: var(--border-whisper);
  border-radius: var(--radius-md);
  box-shadow: var(--shadow-card);
  overflow: hidden;
  transition: box-shadow var(--dur-slow) var(--ease), transform var(--dur-slow) var(--ease);
}
.ds-card:hover {
  box-shadow: var(--shadow-deep);
  transform: translateY(-2px);
}

.card-spine {
  height: 5px;
  background: var(--color-accent);
  opacity: 0.7;
}

.card-body {
  padding: 18px 20px 16px;
}

.card-genre-tag {
  display: inline-flex;
  align-items: center;
  padding: 3px 9px;
  background: var(--badge-bg);
  color: var(--badge-text);
  border-radius: var(--radius-pill);
  font-size: 11px;
  font-weight: var(--fw-semibold);
  letter-spacing: 0.15px;
  margin-bottom: var(--space-3);
}

.card-title {
  font-size: var(--text-h4);
  font-weight: var(--fw-bold);
  letter-spacing: var(--ls-h4);
  color: var(--text-primary);
  margin-bottom: var(--space-4);
  line-height: 1.35;
}

.card-meta {
  display: flex;
  flex-direction: column;
  gap: 5px;
}

.card-meta-row {
  display: flex;
  gap: var(--space-2);
  font-size: var(--text-caption);
  line-height: 1.4;
}

.card-meta-key {
  font-weight: var(--fw-semibold);
  color: var(--text-secondary);
  min-width: 90px;
  flex-shrink: 0;
}

.card-meta-value {
  color: var(--text-primary);
}

.card-color-swatch {
  display: inline-block;
  width: 12px;
  height: 12px;
  border-radius: 50%;
  vertical-align: middle;
  margin-left: 4px;
  border: 1px solid rgba(0,0,0,0.12);
}

/* =========================================================
   BACK-TO-TOP BUTTON
   ========================================================= */
#btn-back-to-top {
  position: fixed;
  bottom: 24px;
  right: 24px;
  width: 42px;
  height: 42px;
  border-radius: var(--radius-pill);
  background: var(--bg-surface);
  border: var(--border-medium);
  box-shadow: var(--shadow-deep);
  color: var(--text-secondary);
  cursor: pointer;
  display: none;
  align-items: center;
  justify-content: center;
  font-size: 18px;
  transition: all var(--dur-base) var(--ease);
  z-index: 100;
}
#btn-back-to-top:hover {
  background: var(--bg-warm);
  color: var(--text-primary);
  transform: translateY(-2px);
}
#btn-back-to-top.visible {
  display: flex;
}

/* =========================================================
   RESPONSIVE
   ========================================================= */
@media (max-width: 900px) {
  .main-layout {
    grid-template-columns: 1fr;
  }
  .filter-sidebar {
    position: static;
  }
  .checkbox-grid {
    grid-template-columns: repeat(3, 1fr);
  }
}
@media (max-width: 600px) {
  .container {
    padding: 0 var(--space-4);
  }
  .app-nav {
    padding: 10px 16px;
  }
  .hero-section .container {
    padding: 0 var(--space-4);
  }
  .hero-title {
    font-size: 2rem;
  }
  .checkbox-grid {
    grid-template-columns: 1fr 1fr;
  }
  #container-generated-books {
    grid-template-columns: 1fr;
  }
}

.app-nav {
  width: 100%;
  max-width: 1200px;
  margin-inline: auto;
  padding-inline: var(--space-4);
}

@media (min-width: 600px)  { .app-nav { padding-inline: var(--space-5); } }
@media (min-width: 1080px) { .app-nav { padding-inline: var(--space-6); } }
/* =========================================================
   ERROR BANNER (Sprint 2)
   ========================================================= */
#app-error-banner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  padding: 10px 14px;
  /* margin-bottom: var(--space-4); */
  background-color: var(--app-error-banner-bg);
  border: 1px solid var(--app-error-banner-border);
  border-left: 4px solid var(--color-orange);
  border-radius: var(--radius-sm);
  font-size: var(--text-caption);
  color: var(--text-primary);
}
#app-error-banner button {
  background: none;
  border: none;
  font-size: 18px;
  line-height: 1;
  cursor: pointer;
  color: var(--text-secondary);
  padding: 0 4px;
  flex-shrink: 0;
}
#app-error-banner button:hover {
  color: var(--text-primary);
}