----------------------------------------------------- style.css  —  Smart Study Helper -----------------------------------------------------
   



-------------------- Reset&Base --------------------


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

:root {
  /* Colours */
  --c-bg:          #f0f4f9;
  --c-surface:     #ffffff;
  --c-surface-2:   #f8fafc;
  --c-border:      #dbe4f0;
  --c-primary:     #2563eb;
  --c-primary-h:   #1d4ed8;
  --c-primary-dim: #eff6ff;
  --c-accent:      #e0eaff;
  --c-text:        #1e293b;
  --c-text-muted:  #64748b;
  --c-kw:          #1d4ed8;
  --c-correct:     #15803d;
  --c-correct-bg:  #dcfce7;
  --c-wrong:       #b91c1c;
  --c-wrong-bg:    #fee2e2;
  --c-warn:        #92400e;
  --c-warn-bg:     #fef3c7;
  --c-mark:        #fef08a;
  --c-error-bg:    #fff5f5;
  --c-error-border:#fca5a5;

  /* Spacing & shape */
  --radius-sm:  8px;
  --radius:     14px;
  --radius-lg:  20px;
  --shadow-sm:  0 1px 4px rgba(37,99,235,.08);
  --shadow:     0 4px 24px rgba(37,99,235,.10);
  --shadow-lg:  0 8px 40px rgba(37,99,235,.14);

  /* Typography */
  --font: 'Segoe UI', system-ui, -apple-system, BlinkMacSystemFont, sans-serif;
  --font-mono: 'Cascadia Code', 'Fira Code', 'Consolas', monospace;

  /* Layout */
  --sidebar-w: 270px;
  --header-h:  140px;
}


--------------------Dark mode variables --------------------


body.dark {
  --c-bg:          #0f172a;
  --c-surface:     #1e293b;
  --c-surface-2:   #172033;
  --c-border:      #334155;
  --c-primary:     #60a5fa;
  --c-primary-h:   #93c5fd;
  --c-primary-dim: #1e3a5f;
  --c-accent:      #1e3a5f;
  --c-text:        #e2e8f0;
  --c-text-muted:  #94a3b8;
  --c-kw:          #93c5fd;
  --c-correct:     #4ade80;
  --c-correct-bg:  #052e16;
  --c-wrong:       #f87171;
  --c-wrong-bg:    #450a0a;
  --c-warn-bg:     #292000;
  --c-mark:        #713f12;
  --c-error-bg:    #1c0a0a;
  --c-error-border:#7f1d1d;
}

body {
  font-family: var(--font);
  background:  var(--c-bg);
  color:        var(--c-text);
  min-height:   100vh;
  line-height:  1.6;
  transition:   background .25s, color .25s;
}

a { color: var(--c-primary); }
button { font-family: var(--font); cursor: pointer; }

-------------------- Header --------------------


.site-header {
  background: linear-gradient(135deg, #1e3a8a 0%, #2563eb 55%, #3b82f6 100%);
  color: #fff;
  padding: 1.8rem 1.5rem 4.5rem;
  text-align: center;
  position: relative;
}

.header-top {
  display: flex;
  align-items: center;
  justify-content: space-between;
  max-width: 1100px;
  margin: 0 auto 1rem;
}

.header-brand h1 {
  font-size: clamp(1.4rem, 3.5vw, 2rem);
  font-weight: 800;
  letter-spacing: -.5px;
}
.header-brand p {
  font-size: .85rem;
  opacity: .8;
  margin-top: .2rem;
}

.header-controls {
  display: flex;
  gap: .5rem;
  align-items: center;
}

.icon-btn {
  background: rgba(255,255,255,.15);
  border: 1.5px solid rgba(255,255,255,.3);
  color: #fff;
  border-radius: 50%;
  width: 38px;
  height: 38px;
  font-size: 1.1rem;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: background .2s;
}
.icon-btn:hover { background: rgba(255,255,255,.28); }


-------------------- Search bar --------------------


.search-wrap {
  position: absolute;
  bottom: -1.5rem;
  left: 50%;
  transform: translateX(-50%);
  width: min(680px, 90%);
  z-index: 20;
}

.search-box {
  display: flex;
  background: var(--c-surface);
  border-radius: 50px;
  box-shadow: var(--shadow-lg);
  border: 2px solid transparent;
  overflow: hidden;
  transition: border-color .2s;
}
.search-box:focus-within { border-color: var(--c-primary); }

#searchInput {
  flex: 1;
  border: none;
  outline: none;
  padding: .9rem 1.3rem;
  font-size: 1rem;
  color: var(--c-text);
  background: transparent;
}
#searchInput::placeholder { color: #a0aec0; }
#searchInput.shake { animation: shake .35s ease; }

@keyframes shake {
  0%,100% { transform: translateX(0); }
  25%      { transform: translateX(-6px); }
  75%      { transform: translateX(6px); }
}

#searchBtn {
  background: var(--c-primary);
  color: #fff;
  border: none;
  padding: .9rem 1.8rem;
  font-size: .95rem;
  font-weight: 700;
  border-radius: 0 50px 50px 0;
  transition: background .2s, transform .1s;
  white-space: nowrap;
  letter-spacing: .01em;
}
#searchBtn:hover  { background: var(--c-primary-h); }
#searchBtn:active { transform: scale(.97); }

.search-hint {
  text-align: center;
  font-size: .75rem;
  color: rgba(255,255,255,.6);
  margin-top: .6rem;
}


-------------------- Layout --------------------


.layout {
  display: flex;
  gap: 1.5rem;
  max-width: 1200px;
  margin: 4rem auto 3rem;
  padding: 0 1rem;
  align-items: flex-start;
}


-------------------- Main content --------------------


#main {
  flex: 1;
  min-width: 0;
}


-------------------- Sidebar --------------------


#sidebar {
  width: var(--sidebar-w);
  flex-shrink: 0;
  background: var(--c-surface);
  border-radius: var(--radius);
  border: 1px solid var(--c-border);
  box-shadow: var(--shadow-sm);
  position: sticky;
  top: 1rem;
  max-height: calc(100vh - 2rem);
  overflow-y: auto;
}

.sidebar-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 1rem 1.1rem .75rem;
  border-bottom: 1px solid var(--c-border);
  position: sticky;
  top: 0;
  background: var(--c-surface);
  z-index: 1;
}
.sidebar-heading {
  font-size: .9rem;
  font-weight: 700;
  color: var(--c-text);
}
.sidebar-count {
  background: var(--c-primary);
  color: #fff;
  font-size: .7rem;
  font-weight: 700;
  border-radius: 50px;
  padding: .1rem .5rem;
  min-width: 22px;
  text-align: center;
}
.sidebar-empty {
  padding: 1.2rem 1.1rem;
  font-size: .82rem;
  color: var(--c-text-muted);
  line-height: 1.6;
}

.saved-list { list-style: none; }

.saved-item {
  display: flex;
  align-items: center;
  gap: .65rem;
  padding: .65rem 1rem;
  cursor: pointer;
  border-bottom: 1px solid var(--c-border);
  transition: background .15s;
}
.saved-item:hover { background: var(--c-primary-dim); }
.saved-item:last-child { border-bottom: none; }

.saved-thumb {
  width: 36px; height: 36px;
  border-radius: 6px;
  object-fit: cover;
  flex-shrink: 0;
}
.saved-placeholder {
  width: 36px; height: 36px;
  border-radius: 6px;
  background: linear-gradient(135deg, #c7d2fe, #a5b4fc);
  color: #3730a3;
  font-weight: 700;
  font-size: .85rem;
  display: flex;
  align-items: center;
  justify-content: center;
  flex-shrink: 0;
}

.saved-info    { flex: 1; min-width: 0; }
.saved-title   { font-size: .82rem; font-weight: 700; color: var(--c-text); overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }
.saved-desc    { font-size: .7rem; color: var(--c-text-muted); overflow: hidden; text-overflow: ellipsis; white-space: nowrap; margin-top: 1px; }

.remove-btn {
  background: none;
  border: none;
  color: var(--c-text-muted);
  font-size: .8rem;
  padding: .2rem .35rem;
  border-radius: 4px;
  flex-shrink: 0;
  transition: color .15s, background .15s;
}
.remove-btn:hover { color: var(--c-wrong); background: var(--c-wrong-bg); }


-------------------- Empty state --------------------


.empty-state {
  text-align: center;
  padding: 5rem 1.5rem;
  color: var(--c-text-muted);
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 1rem;
}
.empty-state svg  { opacity: .25; color: var(--c-text-muted); }
.empty-state h2   { font-size: 1.3rem; font-weight: 700; color: var(--c-text); }
.empty-state p    { font-size: .9rem; max-width: 360px; }


-------------------- Spinner --------------------


.spinner-wrap {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 1rem;
  padding: 5rem 1rem;
  color: var(--c-text-muted);
  font-size: .95rem;
}
.spinner {
  width: 44px; height: 44px;
  border: 4px solid var(--c-border);
  border-top-color: var(--c-primary);
  border-radius: 50%;
  animation: spin .7s linear infinite;
}
@keyframes spin { to { transform: rotate(360deg); } }


-------------------- Error card --------------------


.error-card {
  background: var(--c-error-bg);
  border: 1.5px solid var(--c-error-border);
  border-radius: var(--radius);
  padding: 1.5rem 1.6rem;
  display: flex;
  gap: 1rem;
  align-items: flex-start;
  animation: fadeUp .3s ease;
}
.error-icon   { font-size: 1.6rem; flex-shrink: 0; line-height: 1; }
.error-body h3 { font-size: 1rem; font-weight: 700; color: var(--c-wrong); }
.error-body p  { font-size: .88rem; color: var(--c-wrong); margin-top: .35rem; opacity: .85; }
.error-hint   { font-style: italic; font-size: .82rem !important; }
.retry-btn {
  margin-top: .9rem;
  background: var(--c-wrong);
  color: #fff;
  border: none;
  border-radius: var(--radius-sm);
  padding: .45rem 1rem;
  font-size: .83rem;
  font-weight: 700;
  transition: opacity .15s;
}
.retry-btn:hover { opacity: .85; }


-------------------- Breadcrumb --------------------


.breadcrumb {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: .3rem;
  margin-bottom: .9rem;
  font-size: .8rem;
  color: var(--c-text-muted);
}
.bread-home,
.bread-item {
  color: var(--c-primary);
  cursor: pointer;
  font-weight: 600;
  padding: .1rem .3rem;
  border-radius: 4px;
  transition: background .15s;
}
.bread-home:hover,
.bread-item:hover { background: var(--c-accent); }
.bread-sep     { color: var(--c-border); }
.bread-current { font-weight: 700; color: var(--c-text); }


-------------------- Result card --------------------


.result-card {
  background: var(--c-surface);
  border-radius: var(--radius);
  border: 1px solid var(--c-border);
  box-shadow: var(--shadow);
  overflow: hidden;
  animation: fadeUp .35s ease;
}

@keyframes fadeUp {
  from { opacity: 0; transform: translateY(16px); }
  to   { opacity: 1; transform: translateY(0); }
}


-------------------- Result header (image + meta) --------------------


.result-header {
  display: flex;
  gap: 1.4rem;
  padding: 1.6rem 1.8rem;
  align-items: flex-start;
  border-bottom: 1px solid var(--c-border);
  background: var(--c-surface-2);
}

.result-thumb {
  width: 140px;
  height: 140px;
  object-fit: cover;
  border-radius: var(--radius-sm);
  flex-shrink: 0;
  box-shadow: 0 2px 12px rgba(0,0,0,.12);
  background: var(--c-border);
}

.result-meta     { flex: 1; min-width: 0; }
.result-title    { font-size: clamp(1.2rem, 2.5vw, 1.6rem); font-weight: 800; line-height: 1.2; margin-bottom: .3rem; }
.result-desc     { font-size: .85rem; color: var(--c-text-muted); font-style: italic; margin-bottom: .8rem; }

.result-actions {
  display: flex;
  align-items: center;
  flex-wrap: wrap;
  gap: .6rem;
}

.wiki-link {
  display: inline-flex;
  align-items: center;
  gap: .35rem;
  font-size: .82rem;
  font-weight: 700;
  color: var(--c-primary);
  text-decoration: none;
  padding: .35rem .75rem;
  border: 1.5px solid var(--c-primary);
  border-radius: 50px;
  transition: background .15s, color .15s;
}
.wiki-link:hover { background: var(--c-primary); color: #fff; }

.save-btn {
  background: var(--c-surface);
  border: 1.5px solid var(--c-border);
  color: var(--c-text);
  border-radius: 50px;
  padding: .35rem .9rem;
  font-size: .82rem;
  font-weight: 700;
  transition: all .15s;
}
.save-btn:hover   { border-color: var(--c-primary); color: var(--c-primary); }
.save-btn.is-saved {
  background: var(--c-primary);
  border-color: var(--c-primary);
  color: #fff;
}


-------------------- Result body --------------------


.result-body { padding: 1.4rem 1.8rem 1.8rem; }

.section-row {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: .4rem;
  margin-bottom: .6rem;
}

.section-label {
  font-size: .72rem;
  font-weight: 800;
  text-transform: uppercase;
  letter-spacing: .09em;
  color: var(--c-text-muted);
}

.hint-text {
  font-size: .72rem;
  color: var(--c-text-muted);
  font-style: italic;
}


-------------------- Filter bar --------------------


.filter-wrap {
  margin-bottom: .85rem;
}

#filterInput {
  width: 100%;
  border: 1.5px solid var(--c-border);
  background: var(--c-surface-2);
  color: var(--c-text);
  border-radius: 50px;
  padding: .55rem 1rem;
  font-size: .88rem;
  outline: none;
  transition: border-color .2s;
}
#filterInput:focus { border-color: var(--c-primary); background: var(--c-surface); }
#filterInput::placeholder { color: #a0aec0; }


-------------------- Summary text --------------------


.summary-text {
  font-size: .975rem;
  line-height: 1.8;
  color: var(--c-text);
}
.summary-text b.kw { color: var(--c-kw); font-weight: 700; }
.summary-text mark {
  background: var(--c-mark);
  border-radius: 3px;
  padding: 0 2px;
}


-------------------- Divider --------------------


.divider {
  border: none;
  border-top: 1px solid var(--c-border);
  margin: 1.4rem 0;
}


-------------------- Related topic chips --------------------


.related-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(195px, 1fr));
  gap: .7rem;
  margin-top: .7rem;
}

.related-chip {
  display: flex;
  align-items: center;
  gap: .6rem;
  background: var(--c-primary-dim);
  border: 1.5px solid var(--c-border);
  border-radius: var(--radius-sm);
  padding: .6rem .8rem;
  cursor: pointer;
  transition: all .18s;
  text-align: left;
}
.related-chip:hover {
  background: var(--c-accent);
  border-color: var(--c-primary);
  transform: translateY(-2px);
  box-shadow: 0 4px 14px rgba(37,99,235,.15);
}
.related-chip:focus-visible {
  outline: 2px solid var(--c-primary);
  outline-offset: 2px;
}

.chip-thumb {
  width: 40px; height: 40px;
  border-radius: 6px;
  object-fit: cover;
  flex-shrink: 0;
  background: var(--c-border);
}
.chip-placeholder {
  width: 40px; height: 40px;
  border-radius: 6px;
  background: linear-gradient(135deg, #c7d2fe, #a5b4fc);
  color: #3730a3;
  font-weight: 800;
  font-size: .9rem;
  display: flex;
  align-items: center;
  justify-content: center;
  flex-shrink: 0;
}

.chip-info  { min-width: 0; }
.chip-title { font-size: .82rem; font-weight: 700; color: #1e40af; overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }
.chip-desc  { font-size: .7rem; color: var(--c-text-muted); overflow: hidden; text-overflow: ellipsis; white-space: nowrap; margin-top: 2px; }

body.dark .chip-title    { color: var(--c-primary); }
body.dark .chip-placeholder { background: linear-gradient(135deg, #1e3a8a, #2563eb); color: #bfdbfe; }


-------------------- Quiz section --------------------


.quiz-row {
  display: flex;
  align-items: center;
  gap: 1rem;
  flex-wrap: wrap;
}

.quiz-btn {
  background: linear-gradient(135deg, #7c3aed, #6d28d9);
  color: #fff;
  border: none;
  border-radius: 50px;
  padding: .6rem 1.4rem;
  font-size: .9rem;
  font-weight: 700;
  transition: opacity .2s, transform .1s;
  box-shadow: 0 2px 12px rgba(109,40,217,.3);
}
.quiz-btn:hover  { opacity: .88; }
.quiz-btn:active { transform: scale(.97); }

.quiz-hint {
  font-size: .8rem;
  color: var(--c-text-muted);
  font-style: italic;
}

.quiz-panel {
  margin-top: 1.2rem;
  display: flex;
  flex-direction: column;
  gap: 1rem;
  animation: fadeUp .3s ease;
}
.quiz-panel.hidden { display: none; }

.quiz-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: .7rem 1rem;
  background: linear-gradient(135deg, #f5f3ff, #ede9fe);
  border-radius: var(--radius-sm);
  border: 1px solid #ddd6fe;
}
body.dark .quiz-header { background: #2e1065; border-color: #4c1d95; }

.quiz-title  { font-size: .85rem; font-weight: 700; color: #5b21b6; }
body.dark .quiz-title { color: #c4b5fd; }

.quiz-score { font-size: .82rem; font-weight: 700; }
.score-good { color: var(--c-correct); }
.score-mid  { color: #d97706; }
.score-low  { color: var(--c-wrong); }

.quiz-form {
  background: var(--c-surface-2);
  border: 1.5px solid var(--c-border);
  border-radius: var(--radius-sm);
  padding: 1rem 1.1rem;
  transition: border-color .2s;
}
.quiz-form:focus-within { border-color: #7c3aed; }

.quiz-question {
  font-size: .92rem;
  font-weight: 600;
  color: var(--c-text);
  line-height: 1.5;
  margin-bottom: .8rem;
}
.q-num {
  display: inline-block;
  background: #7c3aed;
  color: #fff;
  font-size: .7rem;
  font-weight: 800;
  border-radius: 4px;
  padding: .1rem .4rem;
  margin-right: .4rem;
  vertical-align: middle;
}

.quiz-options { display: flex; flex-direction: column; gap: .5rem; }

.quiz-option {
  display: flex;
  align-items: center;
  gap: .6rem;
  padding: .55rem .8rem;
  border-radius: var(--radius-sm);
  border: 1.5px solid var(--c-border);
  cursor: pointer;
  font-size: .88rem;
  transition: all .15s;
  background: var(--c-surface);
}
.quiz-option:hover        { border-color: #7c3aed; background: #f5f3ff; }
body.dark .quiz-option:hover { background: #2e1065; }

.quiz-option input[type=radio] { accent-color: #7c3aed; width: 16px; height: 16px; flex-shrink: 0; }

.quiz-option.option-correct { border-color: var(--c-correct) !important; background: var(--c-correct-bg) !important; }
.quiz-option.option-correct .option-text { color: var(--c-correct); font-weight: 700; }
.quiz-option.option-wrong   { border-color: var(--c-wrong)   !important; background: var(--c-wrong-bg)   !important; }
.quiz-option.option-wrong   .option-text { color: var(--c-wrong);   font-weight: 700; }

.quiz-actions { margin-top: .75rem; }

.check-btn {
  background: #7c3aed;
  color: #fff;
  border: none;
  border-radius: var(--radius-sm);
  padding: .45rem 1.1rem;
  font-size: .83rem;
  font-weight: 700;
  transition: opacity .15s;
}
.check-btn:hover    { opacity: .85; }
.check-btn:disabled { opacity: .45; cursor: not-allowed; }

.quiz-feedback {
  margin-top: .65rem;
  font-size: .85rem;
  font-weight: 700;
  min-height: 1.2rem;
}
.quiz-feedback.correct   { color: var(--c-correct); }
.quiz-feedback.incorrect { color: var(--c-wrong); }
.quiz-feedback.warn      { color: var(--c-warn); }

.quiz-empty {
  padding: 1.2rem;
  background: var(--c-surface-2);
  border: 1.5px solid var(--c-border);
  border-radius: var(--radius-sm);
  font-size: .88rem;
  color: var(--c-text-muted);
  text-align: center;
  font-style: italic;
}


-------------------- Definition tooltip --------------------


.def-tooltip {
  position: fixed;
  bottom: 1.5rem;
  left: 50%;
  transform: translateX(-50%) translateY(10px);
  background: var(--c-text);
  color: var(--c-surface);
  border-radius: var(--radius-sm);
  padding: .8rem 1.1rem;
  max-width: min(380px, 90vw);
  box-shadow: var(--shadow-lg);
  opacity: 0;
  pointer-events: none;
  transition: opacity .2s, transform .2s;
  z-index: 999;
}
.def-tooltip.visible {
  opacity: 1;
  transform: translateX(-50%) translateY(0);
  pointer-events: auto;
}
.tip-word { display: block; font-size: .9rem; margin-bottom: .3rem; color: #93c5fd; }
.tip-def  { font-size: .82rem; line-height: 1.5; opacity: .9; }
.tip-close {
  position: absolute;
  top: .4rem; right: .5rem;
  background: none;
  border: none;
  color: rgba(255,255,255,.6);
  font-size: .75rem;
  padding: .1rem .3rem;
  border-radius: 3px;
}
.tip-close:hover { color: #fff; background: rgba(255,255,255,.1); }


-------------------- Responsive --------------------

/* Tablet: collapse sidebar behind toggle */
@media (max-width: 860px) {
  .layout { margin-top: 3.5rem; padding: 0 .75rem; }

  #sidebar {
    position: fixed;
    top: 0; right: -100%;
    width: min(var(--sidebar-w), 85vw);
    height: 100vh;
    max-height: 100vh;
    border-radius: 0;
    z-index: 100;
    box-shadow: var(--shadow-lg);
    transition: right .3s ease;
  }
  .layout.sidebar-open #sidebar { right: 0; }

  /* Overlay */
  .layout.sidebar-open::before {
    content: '';
    position: fixed;
    inset: 0;
    background: rgba(0,0,0,.4);
    z-index: 99;
  }

  #sidebarToggle { display: flex; }
}

@media (min-width: 861px) {
  #sidebarToggle { display: none; }
}

/* Mobile */
@media (max-width: 560px) {
  .result-header        { flex-direction: column; }
  .result-thumb         { width: 100%; height: 200px; }
  .related-grid         { grid-template-columns: 1fr 1fr; }
  .result-body          { padding: 1.1rem; }
  .result-header        { padding: 1.1rem; }
  #searchBtn            { padding: .9rem 1.1rem; }
}

/* Focus styles for accessibility */
:focus-visible {
  outline: 2px solid var(--c-primary);
  outline-offset: 2px;
}