/* ── DESIGN TOKENS ── */
:root {
  --bg:          #F0F4FF;
  --bg-card:     #FFFFFF;
  --bg-deep:     #0A0E1A;
  --primary:     #4F46E5;
  --primary-lt:  #6366F1;
  --accent:      #06D6A0;
  --accent2:     #FFD60A;
  --danger:      #EF4444;
  --success:     #10B981;
  --text:        #0F172A;
  --text-muted:  #64748B;
  --text-light:  #94A3B8;
  --border:      #E2E8F0;
  --border-focus:#4F46E5;
  --code-bg:     #0D1117;
  --code-text:   #E6EDF3;
  --radius:      16px;
  --radius-sm:   10px;
  --shadow:      0 4px 24px rgba(79,70,229,0.10);
  --shadow-lg:   0 12px 48px rgba(79,70,229,0.18);
  --font-main:   'Outfit', sans-serif;
  --font-mono:   'Space Mono', monospace;
}

/* ── RESET ── */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
html { scroll-behavior: smooth; }
body {
  font-family: var(--font-main);
  background: var(--bg);
  color: var(--text);
  min-height: 100vh;
  overflow-x: hidden;
}

/* ── HEADER ── */
.site-header {
  position: sticky;
  top: 0;
  z-index: 100;
  background: rgba(255,255,255,0.85);
  backdrop-filter: blur(16px);
  border-bottom: 1px solid var(--border);
}
.header-inner {
  max-width: 1100px;
  margin: 0 auto;
  padding: 0 24px;
  height: 64px;
  display: flex;
  align-items: center;
  justify-content: space-between;
}
.logo {
  display: flex;
  align-items: center;
  gap: 10px;
  font-size: 1.35rem;
  font-weight: 800;
  letter-spacing: -0.5px;
  color: var(--text);
}
.logo-icon {
  font-size: 1.6rem;
  color: var(--primary);
  animation: spin-slow 8s linear infinite;
}
@keyframes spin-slow {
  from { transform: rotate(0deg); }
  to   { transform: rotate(360deg); }
}
.logo-accent { color: var(--primary); }
.badge-ai {
  background: linear-gradient(135deg, var(--primary), var(--primary-lt));
  color: #fff;
  font-size: 0.75rem;
  font-weight: 600;
  padding: 5px 14px;
  border-radius: 999px;
  letter-spacing: 0.3px;
}

/* ── HERO ── */
.hero {
  position: relative;
  overflow: hidden;
  background: linear-gradient(135deg, #0A0E1A 0%, #1E1B4B 50%, #0A0E1A 100%);
  padding: 80px 24px 72px;
  text-align: center;
}
.hero-bg-grid {
  position: absolute;
  inset: 0;
  background-image:
    linear-gradient(rgba(99,102,241,0.15) 1px, transparent 1px),
    linear-gradient(90deg, rgba(99,102,241,0.15) 1px, transparent 1px);
  background-size: 48px 48px;
  mask-image: radial-gradient(ellipse 80% 80% at 50% 50%, black 40%, transparent 100%);
}
.hero-content {
  position: relative;
  max-width: 760px;
  margin: 0 auto;
}
.hero-tag {
  display: inline-block;
  background: rgba(6,214,160,0.15);
  border: 1px solid rgba(6,214,160,0.4);
  color: var(--accent);
  font-size: 0.78rem;
  font-weight: 600;
  letter-spacing: 1.5px;
  text-transform: uppercase;
  padding: 6px 18px;
  border-radius: 999px;
  margin-bottom: 24px;
}
.hero-title {
  font-size: clamp(2.4rem, 5vw, 3.8rem);
  font-weight: 800;
  color: #fff;
  line-height: 1.1;
  letter-spacing: -1.5px;
  margin-bottom: 20px;
}
.hero-title-accent {
  background: linear-gradient(90deg, var(--accent), var(--accent2));
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}
.hero-sub {
  font-size: 1.1rem;
  color: rgba(255,255,255,0.65);
  line-height: 1.7;
  max-width: 580px;
  margin: 0 auto 32px;
}
.hero-chips {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  justify-content: center;
}
.chip {
  background: rgba(255,255,255,0.08);
  border: 1px solid rgba(255,255,255,0.15);
  color: rgba(255,255,255,0.75);
  font-size: 0.8rem;
  font-weight: 500;
  padding: 6px 16px;
  border-radius: 999px;
  transition: all 0.2s;
}
.chip:hover {
  background: rgba(99,102,241,0.25);
  border-color: var(--primary-lt);
  color: #fff;
}

/* ── APP SHELL ── */
.app-shell {
  max-width: 900px;
  margin: 0 auto;
  padding: 48px 24px 80px;
  display: flex;
  flex-direction: column;
  gap: 32px;
}

/* ── APP CARD ── */
.app-card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 36px;
  box-shadow: var(--shadow);
  transition: box-shadow 0.3s;
  animation: card-in 0.4s ease both;
}
.app-card:hover { box-shadow: var(--shadow-lg); }
@keyframes card-in {
  from { opacity: 0; transform: translateY(20px); }
  to   { opacity: 1; transform: translateY(0); }
}
.app-card.hidden { display: none; }

.card-header {
  display: flex;
  align-items: flex-start;
  gap: 18px;
  margin-bottom: 28px;
  flex-wrap: wrap;
}
.card-header > div:last-child { margin-left: auto; }
.step-badge {
  width: 44px;
  height: 44px;
  border-radius: 12px;
  background: linear-gradient(135deg, var(--primary), var(--primary-lt));
  color: #fff;
  font-size: 0.85rem;
  font-weight: 800;
  font-family: var(--font-mono);
  display: flex;
  align-items: center;
  justify-content: center;
  flex-shrink: 0;
  box-shadow: 0 4px 12px rgba(79,70,229,0.35);
}
.card-title {
  font-size: 1.25rem;
  font-weight: 700;
  color: var(--text);
  margin-bottom: 4px;
}
.card-desc {
  font-size: 0.88rem;
  color: var(--text-muted);
}
.card-actions {
  display: flex;
  gap: 10px;
  flex-wrap: wrap;
}

/* ── FILE DROP ZONE ── */
.file-drop-zone {
  border: 2px dashed var(--border);
  border-radius: var(--radius-sm);
  padding: 36px 24px;
  text-align: center;
  cursor: pointer;
  transition: all 0.25s;
  background: #FAFBFF;
}
.file-drop-zone:hover,
.file-drop-zone.drag-over {
  border-color: var(--primary);
  background: rgba(79,70,229,0.04);
}
.drop-icon { font-size: 2.2rem; margin-bottom: 10px; }
.drop-label {
  font-size: 0.95rem;
  color: var(--text-muted);
  margin-bottom: 6px;
}
.drop-link {
  color: var(--primary);
  font-weight: 600;
  cursor: pointer;
  text-decoration: underline;
  text-underline-offset: 3px;
}
.drop-hint {
  font-size: 0.78rem;
  color: var(--text-light);
  font-family: var(--font-mono);
}

/* ── DIVIDER ── */
.input-divider {
  display: flex;
  align-items: center;
  gap: 16px;
  color: var(--text-light);
  font-size: 0.8rem;
  font-weight: 500;
  text-transform: uppercase;
  letter-spacing: 1px;
  margin: 20px 0;
}
.input-divider::before,
.input-divider::after {
  content: '';
  flex: 1;
  height: 1px;
  background: var(--border);
}

/* ── TEXTAREA ── */
.textarea-wrapper {
  position: relative;
}
.problem-textarea {
  width: 100%;
  padding: 18px 20px;
  font-family: var(--font-mono);
  font-size: 0.85rem;
  line-height: 1.7;
  color: var(--text);
  background: #FAFBFF;
  border: 1.5px solid var(--border);
  border-radius: var(--radius-sm);
  resize: vertical;
  transition: border-color 0.2s, box-shadow 0.2s;
  outline: none;
}
.problem-textarea:focus {
  border-color: var(--border-focus);
  box-shadow: 0 0 0 3px rgba(79,70,229,0.12);
  background: #fff;
}
.problem-textarea::placeholder { color: var(--text-light); }
.textarea-footer {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-top: 8px;
  padding: 0 4px;
}
.char-count {
  font-size: 0.75rem;
  color: var(--text-light);
  font-family: var(--font-mono);
}
.btn-clear {
  background: none;
  border: none;
  color: var(--text-light);
  font-size: 0.78rem;
  cursor: pointer;
  font-family: var(--font-main);
  transition: color 0.2s;
}
.btn-clear:hover { color: var(--danger); }

/* ── FILE PREVIEW ── */
.file-preview {
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  overflow: hidden;
  margin-top: 16px;
}
.file-preview-header {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 12px 16px;
  background: #F8FAFC;
  border-bottom: 1px solid var(--border);
}
.file-icon { font-size: 1.1rem; }
.file-name {
  flex: 1;
  font-size: 0.88rem;
  font-weight: 600;
  color: var(--text);
  font-family: var(--font-mono);
}
.btn-remove-file {
  background: none;
  border: none;
  color: var(--text-light);
  cursor: pointer;
  font-size: 0.9rem;
  padding: 2px 6px;
  border-radius: 4px;
  transition: all 0.2s;
}
.btn-remove-file:hover { background: #FEE2E2; color: var(--danger); }
.file-content-preview {
  padding: 16px;
  font-family: var(--font-mono);
  font-size: 0.78rem;
  line-height: 1.6;
  color: var(--text-muted);
  max-height: 160px;
  overflow-y: auto;
  background: #FAFBFF;
  white-space: pre-wrap;
  word-break: break-word;
}

/* ── API KEY ── */
.api-key-row {
  display: flex;
  align-items: center;
  gap: 14px;
  margin-top: 24px;
  flex-wrap: wrap;
}
.api-label {
  font-size: 0.88rem;
  font-weight: 600;
  color: var(--text);
  white-space: nowrap;
  display: flex;
  align-items: center;
  gap: 6px;
}
.api-input {
  flex: 1;
  min-width: 220px;
  padding: 11px 16px;
  font-family: var(--font-mono);
  font-size: 0.85rem;
  border: 1.5px solid var(--border);
  border-radius: var(--radius-sm);
  outline: none;
  transition: border-color 0.2s, box-shadow 0.2s;
  background: #FAFBFF;
  color: var(--text);
}
.api-input:focus {
  border-color: var(--border-focus);
  box-shadow: 0 0 0 3px rgba(79,70,229,0.12);
}
.api-hint {
  font-size: 0.72rem;
  color: var(--text-light);
  width: 100%;
  padding-left: 2px;
}

/* ── BUTTONS ── */
.btn-solve {
  width: 100%;
  margin-top: 28px;
  padding: 18px 32px;
  background: linear-gradient(135deg, var(--primary) 0%, var(--primary-lt) 100%);
  color: #fff;
  border: none;
  border-radius: var(--radius-sm);
  font-family: var(--font-main);
  font-size: 1.05rem;
  font-weight: 700;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 10px;
  transition: all 0.25s;
  box-shadow: 0 6px 24px rgba(79,70,229,0.35);
  letter-spacing: 0.3px;
}
.btn-solve:hover {
  transform: translateY(-2px);
  box-shadow: 0 10px 32px rgba(79,70,229,0.45);
}
.btn-solve:active { transform: translateY(0); }
.btn-solve:disabled {
  opacity: 0.55;
  cursor: not-allowed;
  transform: none;
}
.btn-run {
  margin-top: 24px;
  padding: 14px 32px;
  background: linear-gradient(135deg, var(--accent) 0%, #00B894 100%);
  color: #0A0E1A;
  border: none;
  border-radius: var(--radius-sm);
  font-family: var(--font-main);
  font-size: 0.95rem;
  font-weight: 700;
  cursor: pointer;
  display: inline-flex;
  align-items: center;
  gap: 8px;
  transition: all 0.25s;
  box-shadow: 0 4px 16px rgba(6,214,160,0.35);
}
.btn-run:hover {
  transform: translateY(-2px);
  box-shadow: 0 8px 24px rgba(6,214,160,0.45);
}
.btn-secondary {
  padding: 9px 18px;
  background: #F1F5F9;
  color: var(--text);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  font-family: var(--font-main);
  font-size: 0.83rem;
  font-weight: 600;
  cursor: pointer;
  transition: all 0.2s;
}
.btn-secondary:hover {
  background: var(--primary);
  color: #fff;
  border-color: var(--primary);
}
.btn-reset {
  margin-top: 24px;
  display: block;
}
.btn-icon { font-size: 1.1rem; }

/* ── ANALYSIS GRID ── */
.analysis-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(180px, 1fr));
  gap: 16px;
  margin-bottom: 24px;
}
.analysis-item {
  background: linear-gradient(135deg, #F8FAFF 0%, #EEF2FF 100%);
  border: 1px solid #C7D2FE;
  border-radius: var(--radius-sm);
  padding: 20px;
  transition: transform 0.2s;
}
.analysis-item:hover { transform: translateY(-2px); }
.analysis-label {
  font-size: 0.72rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 1.2px;
  color: var(--primary);
  margin-bottom: 8px;
}
.analysis-value {
  font-size: 1.15rem;
  font-weight: 700;
  color: var(--text);
  font-family: var(--font-mono);
}

/* Problem type gets special highlight */
#problemTypeBox {
  background: linear-gradient(135deg, var(--primary) 0%, var(--primary-lt) 100%);
  border-color: var(--primary);
}
#problemTypeBox .analysis-label { color: rgba(255,255,255,0.75); }
#problemTypeBox .analysis-value { color: #fff; font-size: 1.3rem; }

.model-description-box {
  background: #F8FAFC;
  border: 1px solid var(--border);
  border-left: 4px solid var(--accent);
  border-radius: var(--radius-sm);
  padding: 20px 24px;
}
.model-desc-label {
  font-size: 0.72rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 1.2px;
  color: var(--accent);
  margin-bottom: 10px;
}
.model-desc-text {
  font-size: 0.92rem;
  line-height: 1.75;
  color: var(--text);
}

/* ── CODE BLOCK ── */
.code-block-wrapper {
  position: relative;
  border-radius: var(--radius-sm);
  overflow: hidden;
  border: 1px solid #30363D;
}
.code-lang-tag {
  position: absolute;
  top: 12px;
  right: 16px;
  font-family: var(--font-mono);
  font-size: 0.7rem;
  color: rgba(255,255,255,0.35);
  letter-spacing: 0.5px;
}
.code-block {
  background: var(--code-bg);
  color: var(--code-text);
  font-family: var(--font-mono);
  font-size: 0.82rem;
  line-height: 1.75;
  padding: 28px 24px;
  overflow-x: auto;
  white-space: pre;
  max-height: 480px;
  overflow-y: auto;
}
/* Syntax-like colouring via spans injected by JS */
.code-block .kw  { color: #FF7B72; }
.code-block .fn  { color: #D2A8FF; }
.code-block .str { color: #A5D6FF; }
.code-block .cm  { color: #8B949E; font-style: italic; }
.code-block .num { color: #79C0FF; }

/* ── RESULTS ── */
.results-status {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 14px 20px;
  border-radius: var(--radius-sm);
  background: #F8FAFC;
  border: 1px solid var(--border);
  margin-bottom: 24px;
  font-weight: 600;
  font-size: 0.95rem;
}
.status-dot {
  width: 12px;
  height: 12px;
  border-radius: 50%;
  background: var(--text-light);
  flex-shrink: 0;
}
.status-dot.optimal  { background: var(--success); box-shadow: 0 0 8px rgba(16,185,129,0.5); }
.status-dot.infeasible { background: var(--danger); }
.status-dot.unbounded  { background: var(--accent2); }

.results-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(200px, 1fr));
  gap: 14px;
  margin-bottom: 24px;
}
.result-var {
  background: #F8FAFC;
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  padding: 16px 18px;
  display: flex;
  flex-direction: column;
  gap: 4px;
  transition: border-color 0.2s;
}
.result-var:hover { border-color: var(--primary); }
.result-var-name {
  font-family: var(--font-mono);
  font-size: 0.8rem;
  color: var(--text-muted);
}
.result-var-value {
  font-size: 1.3rem;
  font-weight: 700;
  color: var(--primary);
  font-family: var(--font-mono);
}

.objective-result {
  background: linear-gradient(135deg, var(--accent) 0%, #00B894 100%);
  border-radius: var(--radius-sm);
  padding: 24px 28px;
  margin-bottom: 24px;
  display: flex;
  align-items: center;
  justify-content: space-between;
}
.obj-label {
  font-size: 0.85rem;
  font-weight: 700;
  color: rgba(10,14,26,0.7);
  text-transform: uppercase;
  letter-spacing: 1px;
}
.obj-value {
  font-size: 2rem;
  font-weight: 800;
  color: #0A0E1A;
  font-family: var(--font-mono);
}

.solver-output-box {
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  overflow: hidden;
}
.solver-output-label {
  padding: 10px 16px;
  background: #F1F5F9;
  font-size: 0.75rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 1px;
  color: var(--text-muted);
  border-bottom: 1px solid var(--border);
}
.solver-output {
  padding: 16px;
  font-family: var(--font-mono);
  font-size: 0.78rem;
  line-height: 1.7;
  color: var(--text-muted);
  background: #FAFBFF;
  max-height: 220px;
  overflow-y: auto;
  white-space: pre-wrap;
  word-break: break-word;
}

/* ── LOADING OVERLAY ── */
.loading-overlay {
  position: fixed;
  inset: 0;
  background: rgba(10,14,26,0.75);
  backdrop-filter: blur(8px);
  z-index: 999;
  display: flex;
  align-items: center;
  justify-content: center;
}
.loading-overlay.hidden { display: none; }
.loading-card {
  background: #fff;
  border-radius: var(--radius);
  padding: 48px 40px;
  max-width: 420px;
  width: 90%;
  text-align: center;
  box-shadow: 0 24px 80px rgba(0,0,0,0.3);
  animation: card-in 0.3s ease;
}
.loading-spinner {
  width: 52px;
  height: 52px;
  border: 4px solid #EEF2FF;
  border-top-color: var(--primary);
  border-radius: 50%;
  animation: spin 0.8s linear infinite;
  margin: 0 auto 24px;
}
@keyframes spin {
  to { transform: rotate(360deg); }
}
.loading-title {
  font-size: 1.2rem;
  font-weight: 700;
  color: var(--text);
  margin-bottom: 8px;
}
.loading-sub {
  font-size: 0.88rem;
  color: var(--text-muted);
  margin-bottom: 28px;
}
.loading-steps {
  display: flex;
  flex-direction: column;
  gap: 10px;
  text-align: left;
}
.lstep {
  font-size: 0.85rem;
  color: var(--text-light);
  padding: 10px 14px;
  border-radius: 8px;
  background: #F8FAFC;
  border: 1px solid var(--border);
  transition: all 0.3s;
  font-family: var(--font-mono);
}
.lstep.active {
  color: var(--primary);
  background: #EEF2FF;
  border-color: #C7D2FE;
  font-weight: 600;
}
.lstep.done {
  color: var(--success);
  background: #F0FDF4;
  border-color: #BBF7D0;
}

/* ── TOAST ── */
.toast {
  position: fixed;
  bottom: 32px;
  right: 32px;
  background: var(--text);
  color: #fff;
  padding: 14px 22px;
  border-radius: var(--radius-sm);
  font-size: 0.88rem;
  font-weight: 500;
  z-index: 9999;
  box-shadow: 0 8px 32px rgba(0,0,0,0.25);
  animation: toast-in 0.3s ease;
  max-width: 320px;
}
.toast.hidden { display: none; }
.toast.success { background: var(--success); }
.toast.error   { background: var(--danger); }
@keyframes toast-in {
  from { opacity: 0; transform: translateY(12px); }
  to   { opacity: 1; transform: translateY(0); }
}

/* ── FOOTER ── */
.site-footer {
  text-align: center;
  padding: 28px 24px;
  font-size: 0.82rem;
  color: var(--text-light);
  border-top: 1px solid var(--border);
  background: #fff;
}
.site-footer strong { color: var(--primary); }

/* ── SCROLLBAR ── */
::-webkit-scrollbar { width: 6px; height: 6px; }
::-webkit-scrollbar-track { background: transparent; }
::-webkit-scrollbar-thumb { background: #CBD5E1; border-radius: 3px; }
::-webkit-scrollbar-thumb:hover { background: var(--primary); }

/* ── RESPONSIVE ── */
@media (max-width: 640px) {
  .app-card { padding: 24px 18px; }
  .hero { padding: 56px 20px 52px; }
  .analysis-grid { grid-template-columns: 1fr 1fr; }
  .api-key-row { flex-direction: column; align-items: stretch; }
  .card-header { flex-direction: column; }
  .card-header > div:last-child { margin-left: 0; }
  .objective-result { flex-direction: column; gap: 8px; text-align: center; }
}