/* ============================================================
   S-DES Simulator — Dark Cyber Theme
   Color Palette:
   --clr-bg:       #0a0e1a  (deep navy black)
   --clr-surface:  #111827  (dark surface)
   --clr-card:     #1a2235  (card background)
   --clr-border:   #1e3a5f  (subtle border)
   --clr-accent:   #00f5d4  (cyan-teal)
   --clr-accent2:  #7c3aed  (violet)
   --clr-k1:       #f59e0b  (amber for K1)
   --clr-k2:       #10b981  (emerald for K2)
   --clr-text:     #e2e8f0  (light text)
   --clr-muted:    #64748b  (muted text)
   Signature: glowing bit cells with monospace grid identity
   ============================================================ */

@import url('https://fonts.googleapis.com/css2?family=Inter:wght@300;400;500;600;700&family=JetBrains+Mono:wght@400;600&family=Space+Grotesk:wght@500;700&display=swap');

:root {
  --clr-bg:      #0a0e1a;
  --clr-surface: #111827;
  --clr-card:    #1a2235;
  --clr-card2:   #1e293b;
  --clr-border:  #1e3a5f;
  --clr-border2: #2d4a7a;
  --clr-accent:  #00f5d4;
  --clr-accent2: #7c3aed;
  --clr-k1:      #f59e0b;
  --clr-k2:      #10b981;
  --clr-danger:  #ef4444;
  --clr-text:    #e2e8f0;
  --clr-text2:   #94a3b8;
  --clr-muted:   #64748b;
  --radius:      12px;
  --radius-sm:   8px;
  --shadow:      0 4px 24px rgba(0,0,0,0.4);
  --shadow-glow: 0 0 20px rgba(0,245,212,0.15);
  --font-sans:   'Inter', system-ui, sans-serif;
  --font-mono:   'JetBrains Mono', 'Courier New', monospace;
  --font-display:'Space Grotesk', system-ui, sans-serif;
  --transition:  all 0.25s cubic-bezier(0.4, 0, 0.2, 1);
}

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

html { scroll-behavior: smooth; }

body {
  background: var(--clr-bg);
  color: var(--clr-text);
  font-family: var(--font-sans);
  font-size: 15px;
  line-height: 1.6;
  min-height: 100vh;
  overflow-x: hidden;
}

/* ---- Canvas Particles ---- */
#particles {
  position: fixed;
  top: 0; left: 0;
  width: 100%; height: 100%;
  pointer-events: none;
  z-index: 0;
  opacity: 0.35;
}

/* ---- Layout ---- */
.page-wrapper {
  position: relative;
  z-index: 1;
  max-width: 960px;
  margin: 0 auto;
  padding: 0 20px 80px;
}

/* ---- Header ---- */
.site-header {
  text-align: center;
  padding: 56px 0 40px;
}

.header-badge {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  background: rgba(0,245,212,0.08);
  border: 1px solid rgba(0,245,212,0.2);
  border-radius: 100px;
  padding: 6px 16px;
  font-size: 12px;
  font-family: var(--font-mono);
  color: var(--clr-accent);
  letter-spacing: 0.1em;
  text-transform: uppercase;
  margin-bottom: 20px;
}

.header-badge .dot {
  width: 6px; height: 6px;
  border-radius: 50%;
  background: var(--clr-accent);
  animation: pulse-dot 2s infinite;
}

@keyframes pulse-dot {
  0%, 100% { opacity: 1; transform: scale(1); }
  50% { opacity: 0.4; transform: scale(0.8); }
}

.site-title {
  font-family: var(--font-display);
  font-size: clamp(32px, 6vw, 52px);
  font-weight: 700;
  letter-spacing: -0.02em;
  line-height: 1.1;
  margin-bottom: 12px;
}

.site-title .highlight {
  color: var(--clr-accent);
  position: relative;
}

.site-title .highlight::after {
  content: '';
  position: absolute;
  bottom: 2px;
  left: 0; right: 0;
  height: 2px;
  background: linear-gradient(90deg, var(--clr-accent), transparent);
}

.site-subtitle {
  color: var(--clr-text2);
  font-size: 16px;
  max-width: 480px;
  margin: 0 auto;
}

/* ---- Section titles ---- */
.section-title {
  font-family: var(--font-display);
  font-size: 13px;
  font-weight: 600;
  color: var(--clr-accent);
  letter-spacing: 0.12em;
  text-transform: uppercase;
  margin-bottom: 20px;
  display: flex;
  align-items: center;
  gap: 10px;
}

.section-title::after {
  content: '';
  flex: 1;
  height: 1px;
  background: var(--clr-border);
}

/* ---- Input Card ---- */
.input-card {
  background: var(--clr-card);
  border: 1px solid var(--clr-border);
  border-radius: var(--radius);
  padding: 32px;
  margin-bottom: 24px;
  box-shadow: var(--shadow);
  position: relative;
  overflow: hidden;
}

.input-card::before {
  content: '';
  position: absolute;
  top: 0; left: 0; right: 0;
  height: 2px;
  background: linear-gradient(90deg, var(--clr-accent), var(--clr-accent2));
}

/* ---- Form Grid ---- */
.form-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 20px;
  margin-bottom: 20px;
}

.form-group {
  display: flex;
  flex-direction: column;
  gap: 8px;
}

.form-group.full-width { grid-column: 1 / -1; }

.form-label {
  font-size: 12px;
  font-weight: 600;
  color: var(--clr-text2);
  letter-spacing: 0.08em;
  text-transform: uppercase;
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.bit-counter {
  font-family: var(--font-mono);
  font-size: 11px;
  transition: var(--transition);
}

.form-input,
.form-select {
  background: var(--clr-bg);
  border: 1px solid var(--clr-border);
  border-radius: var(--radius-sm);
  padding: 12px 16px;
  color: var(--clr-text);
  font-family: var(--font-mono);
  font-size: 18px;
  letter-spacing: 0.15em;
  transition: var(--transition);
  outline: none;
  width: 100%;
}

.form-input:focus,
.form-select:focus {
  border-color: var(--clr-accent);
  box-shadow: 0 0 0 3px rgba(0,245,212,0.12);
}

.form-input.input-error {
  border-color: var(--clr-danger);
  box-shadow: 0 0 0 3px rgba(239,68,68,0.12);
}

.form-select {
  font-family: var(--font-sans);
  font-size: 15px;
  letter-spacing: normal;
  cursor: pointer;
  appearance: none;
  background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='12' height='8' fill='none'%3E%3Cpath d='M1 1l5 5 5-5' stroke='%2364748b' stroke-width='1.5' stroke-linecap='round' stroke-linejoin='round'/%3E%3C/svg%3E");
  background-repeat: no-repeat;
  background-position: right 14px center;
  padding-right: 40px;
}

.error-msg {
  font-size: 12px;
  color: var(--clr-danger);
  display: none;
  margin-top: 2px;
}

/* ---- Mode Selector ---- */
.mode-selector {
  display: flex;
  gap: 12px;
}

.mode-option {
  flex: 1;
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 14px 18px;
  border: 1px solid var(--clr-border);
  border-radius: var(--radius-sm);
  cursor: pointer;
  transition: var(--transition);
  background: var(--clr-bg);
}

.mode-option:hover {
  border-color: var(--clr-accent);
  background: rgba(0,245,212,0.04);
}

.mode-option input[type="radio"] { display: none; }

.mode-option.selected {
  border-color: var(--clr-accent);
  background: rgba(0,245,212,0.08);
}

.mode-icon { font-size: 20px; }
.mode-text { font-size: 14px; font-weight: 600; }
.mode-desc { font-size: 11px; color: var(--clr-muted); }

/* ---- Examples ---- */
.examples-row {
  display: flex;
  align-items: center;
  gap: 10px;
  margin-bottom: 24px;
  flex-wrap: wrap;
}

.examples-label {
  font-size: 12px;
  color: var(--clr-muted);
  white-space: nowrap;
}

.example-btn {
  background: rgba(124,58,237,0.1);
  border: 1px solid rgba(124,58,237,0.3);
  border-radius: 6px;
  padding: 5px 12px;
  color: #a78bfa;
  font-size: 12px;
  font-family: var(--font-mono);
  cursor: pointer;
  transition: var(--transition);
}

.example-btn:hover {
  background: rgba(124,58,237,0.2);
  border-color: rgba(124,58,237,0.5);
}

/* ---- Buttons ---- */
.btn-row {
  display: flex;
  gap: 12px;
}

.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  padding: 13px 28px;
  border-radius: var(--radius-sm);
  font-weight: 600;
  font-size: 15px;
  cursor: pointer;
  transition: var(--transition);
  border: none;
  outline: none;
  font-family: var(--font-sans);
}

.btn-primary {
  background: linear-gradient(135deg, var(--clr-accent), #00c4aa);
  color: #0a0e1a;
  box-shadow: 0 0 20px rgba(0,245,212,0.3);
  flex: 1;
}

.btn-primary:hover {
  transform: translateY(-1px);
  box-shadow: 0 0 32px rgba(0,245,212,0.4);
}

.btn-primary:active { transform: translateY(0); }

.btn-secondary {
  background: transparent;
  border: 1px solid var(--clr-border);
  color: var(--clr-text2);
  padding: 13px 24px;
}

.btn-secondary:hover {
  border-color: var(--clr-border2);
  color: var(--clr-text);
}

/* ---- Result Section ---- */
#result-section {
  opacity: 0;
  transform: translateY(20px);
  transition: opacity 0.4s ease, transform 0.4s ease;
  pointer-events: none;
}

#result-section.visible {
  opacity: 1;
  transform: translateY(0);
  pointer-events: all;
}

.result-card {
  background: var(--clr-card);
  border: 1px solid var(--clr-border);
  border-radius: var(--radius);
  padding: 28px 32px;
  margin-bottom: 20px;
  position: relative;
  overflow: hidden;
}

.result-card::before {
  content: '';
  position: absolute;
  top: 0; left: 0; right: 0;
  height: 2px;
  background: linear-gradient(90deg, var(--clr-k2), var(--clr-accent));
}

.result-header {
  display: flex;
  align-items: center;
  gap: 12px;
  margin-bottom: 20px;
}

.result-icon { font-size: 24px; }

.result-title {
  font-family: var(--font-display);
  font-size: 18px;
  font-weight: 700;
}

.result-label {
  font-size: 12px;
  color: var(--clr-muted);
  letter-spacing: 0.1em;
  text-transform: uppercase;
  margin-bottom: 12px;
}

.output-bits-row {
  display: flex;
  gap: 6px;
  margin-bottom: 16px;
  flex-wrap: wrap;
}

.output-bit {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 44px; height: 44px;
  background: rgba(0,245,212,0.08);
  border: 1px solid rgba(0,245,212,0.3);
  border-radius: 8px;
  font-family: var(--font-mono);
  font-size: 20px;
  font-weight: 600;
  color: var(--clr-accent);
  box-shadow: 0 0 8px rgba(0,245,212,0.15);
  animation: bit-appear 0.3s ease forwards;
}

@keyframes bit-appear {
  from { opacity: 0; transform: scale(0.7); }
  to   { opacity: 1; transform: scale(1); }
}

.output-bit:nth-child(1) { animation-delay: 0.05s; }
.output-bit:nth-child(2) { animation-delay: 0.10s; }
.output-bit:nth-child(3) { animation-delay: 0.15s; }
.output-bit:nth-child(4) { animation-delay: 0.20s; }
.output-bit:nth-child(5) { animation-delay: 0.25s; }
.output-bit:nth-child(6) { animation-delay: 0.30s; }
.output-bit:nth-child(7) { animation-delay: 0.35s; }
.output-bit:nth-child(8) { animation-delay: 0.40s; }

.output-string {
  font-family: var(--font-mono);
  font-size: 22px;
  font-weight: 600;
  color: var(--clr-accent);
  letter-spacing: 0.2em;
  padding: 12px 16px;
  background: rgba(0,245,212,0.05);
  border-radius: var(--radius-sm);
  display: inline-block;
}

/* ---- Toggle Solution ---- */
.toggle-btn-wrapper {
  text-align: center;
  margin-bottom: 20px;
}

#toggle-btn {
  background: transparent;
  border: 1px solid var(--clr-border2);
  color: var(--clr-accent);
  border-radius: 100px;
  padding: 10px 28px;
  font-size: 14px;
  font-weight: 500;
  cursor: pointer;
  transition: var(--transition);
  letter-spacing: 0.02em;
}

#toggle-btn:hover {
  background: rgba(0,245,212,0.06);
  border-color: var(--clr-accent);
}

/* ---- Solution Wrapper ---- */
#solution-wrapper {
  overflow: hidden;
  transition: var(--transition);
}

#solution-wrapper.hidden { display: none; }

/* ---- Phase Blocks ---- */
.phase-block {
  margin-bottom: 32px;
}

.phase-title {
  font-family: var(--font-display);
  font-size: 20px;
  font-weight: 700;
  color: var(--clr-text);
  margin-bottom: 16px;
  display: flex;
  align-items: center;
  gap: 10px;
  padding-bottom: 12px;
  border-bottom: 1px solid var(--clr-border);
}

.phase-icon { font-size: 22px; }

/* ---- Step Cards ---- */
.step-card {
  background: var(--clr-card2);
  border: 1px solid var(--clr-border);
  border-radius: var(--radius);
  padding: 20px 24px;
  margin-bottom: 12px;
  display: flex;
  gap: 20px;
  position: relative;
  transition: var(--transition);
}

.step-card:hover {
  border-color: var(--clr-border2);
  box-shadow: 0 2px 12px rgba(0,0,0,0.3);
}

.step-card.accent-k1 { border-left: 3px solid var(--clr-k1); }
.step-card.accent-k2 { border-left: 3px solid var(--clr-k2); }
.step-card.round-card { border-left: 3px solid var(--clr-accent2); }
.step-card.swap-card { border-left: 3px solid #ec4899; }

.step-num {
  flex-shrink: 0;
  width: 36px; height: 36px;
  border-radius: 50%;
  background: rgba(0,245,212,0.08);
  border: 1px solid rgba(0,245,212,0.2);
  display: flex;
  align-items: center;
  justify-content: center;
  font-family: var(--font-mono);
  font-size: 11px;
  font-weight: 600;
  color: var(--clr-accent);
}

.step-num.round-num {
  background: rgba(124,58,237,0.12);
  border-color: rgba(124,58,237,0.3);
  color: #a78bfa;
  font-size: 10px;
}

.step-content { flex: 1; }

.step-heading {
  font-weight: 600;
  font-size: 15px;
  color: var(--clr-text);
  margin-bottom: 14px;
}

/* ---- Step Rows (bit display) ---- */
.step-row {
  display: flex;
  align-items: center;
  gap: 10px;
  margin-bottom: 8px;
  flex-wrap: wrap;
}

.step-label {
  font-size: 12px;
  color: var(--clr-text2);
  min-width: 180px;
  font-family: var(--font-sans);
}

.step-bits {
  display: flex;
  gap: 4px;
}

.step-str {
  font-family: var(--font-mono);
  font-size: 13px;
  color: var(--clr-muted);
  margin-left: 6px;
}

/* ---- Bit Cells ---- */
.bit-cell {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 26px; height: 26px;
  border-radius: 5px;
  font-family: var(--font-mono);
  font-size: 13px;
  font-weight: 600;
  background: rgba(255,255,255,0.04);
  border: 1px solid rgba(255,255,255,0.08);
  color: var(--clr-text);
  transition: var(--transition);
}

.bit-cell.highlight {
  background: rgba(0,245,212,0.15);
  border-color: rgba(0,245,212,0.4);
  color: var(--clr-accent);
}

/* ---- Permutation visual ---- */
.permute-visual { display: flex; flex-direction: column; gap: 4px; }
.permute-arrow { display: flex; align-items: center; gap: 12px; margin: 4px 0; }
.arrow-down { color: var(--clr-muted); font-size: 18px; }
.permute-table-label {
  font-family: var(--font-mono);
  font-size: 11px;
  color: var(--clr-muted);
  padding: 4px 10px;
  background: rgba(255,255,255,0.03);
  border-radius: 4px;
  border: 1px solid var(--clr-border);
  margin: 6px 0;
  display: inline-block;
}

/* ---- Split Visual ---- */
.split-visual {
  display: flex;
  gap: 0;
  align-items: flex-start;
}

.split-part { flex: 1; }
.split-label {
  font-size: 11px;
  font-weight: 600;
  color: var(--clr-accent2);
  letter-spacing: 0.08em;
  text-transform: uppercase;
  margin-bottom: 8px;
}

.split-divider {
  width: 1px;
  background: var(--clr-border);
  margin: 0 20px;
  align-self: stretch;
}

/* ---- Key Summary ---- */
.key-summary {
  display: flex;
  gap: 16px;
  margin-top: 16px;
}

.key-badge {
  flex: 1;
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 14px 18px;
  border-radius: var(--radius-sm);
}

.key-badge.k1-badge {
  background: rgba(245,158,11,0.08);
  border: 1px solid rgba(245,158,11,0.25);
}

.key-badge.k2-badge {
  background: rgba(16,185,129,0.08);
  border: 1px solid rgba(16,185,129,0.25);
}

.key-badge span {
  font-weight: 700;
  font-size: 13px;
  letter-spacing: 0.05em;
}

.key-badge.k1-badge span { color: var(--clr-k1); }
.key-badge.k2-badge span { color: var(--clr-k2); }

.key-badge code {
  font-family: var(--font-mono);
  font-size: 17px;
  letter-spacing: 0.15em;
  color: var(--clr-text);
}

/* ---- F-Function Block ---- */
.f-function-block {
  background: rgba(0,0,0,0.2);
  border: 1px solid var(--clr-border);
  border-radius: var(--radius-sm);
  padding: 16px;
  display: flex;
  flex-direction: column;
  gap: 14px;
  margin-bottom: 14px;
}

.f-inner-step { }

.f-label {
  font-size: 12px;
  font-weight: 600;
  color: var(--clr-accent2);
  letter-spacing: 0.06em;
  text-transform: uppercase;
  margin-bottom: 8px;
}

.xor-line {
  font-family: var(--font-mono);
  font-size: 13px;
  color: var(--clr-accent);
  padding: 4px 0;
  border-top: 1px dashed var(--clr-border);
  margin: 4px 0;
}

.xor-final { background: rgba(0,245,212,0.03); border-radius: var(--radius-sm); padding: 12px; }

/* ---- S-Box Tables ---- */
.sbox-wrapper {
  display: flex;
  gap: 24px;
  flex-wrap: wrap;
}

.sbox-side { flex: 1; min-width: 180px; }

.sbox-input-label {
  font-size: 12px;
  color: var(--clr-text2);
  margin-bottom: 8px;
}

.sbox-table {
  border-collapse: collapse;
  font-family: var(--font-mono);
  font-size: 13px;
  margin-bottom: 8px;
  width: 100%;
}

.sbox-table caption {
  font-weight: 700;
  color: var(--clr-accent);
  font-size: 12px;
  text-align: left;
  margin-bottom: 4px;
  caption-side: top;
  padding-bottom: 4px;
}

.sbox-table th, .sbox-table td {
  border: 1px solid var(--clr-border);
  padding: 6px 10px;
  text-align: center;
}

.sbox-table th {
  background: rgba(0,0,0,0.3);
  color: var(--clr-muted);
  font-size: 11px;
}

.sbox-table td { color: var(--clr-text); }

.sbox-table .sbox-rowlabel {
  color: var(--clr-muted);
  font-size: 11px;
  background: rgba(0,0,0,0.2);
}

.sbox-highlight {
  background: rgba(0,245,212,0.18) !important;
  color: var(--clr-accent) !important;
  font-weight: 700;
  box-shadow: inset 0 0 8px rgba(0,245,212,0.2);
}

.sbox-output {
  font-size: 13px;
  color: var(--clr-text2);
}

.bit-inline {
  font-family: var(--font-mono);
  font-weight: 700;
  color: var(--clr-accent);
  background: rgba(0,245,212,0.08);
  padding: 2px 8px;
  border-radius: 4px;
}

/* ---- Swap Visual ---- */
.swap-visual {
  display: flex;
  align-items: center;
  gap: 20px;
}

.swap-before, .swap-after {
  flex: 1;
  padding: 12px;
  border-radius: var(--radius-sm);
  border: 1px solid var(--clr-border);
  background: rgba(0,0,0,0.2);
}

.swap-tag {
  display: block;
  font-size: 11px;
  color: var(--clr-muted);
  margin-bottom: 6px;
  letter-spacing: 0.06em;
  text-transform: uppercase;
}

.swap-bits {
  font-family: var(--font-mono);
  font-size: 14px;
  color: var(--clr-text);
  display: flex;
  align-items: center;
  gap: 8px;
  margin-bottom: 4px;
}

.swap-arrow {
  font-size: 28px;
  color: #ec4899;
  flex-shrink: 0;
}

/* ---- Split inline ---- */
.split-row-inline {
  display: flex;
  gap: 20px;
  margin-top: 10px;
  font-family: var(--font-mono);
  font-size: 14px;
  color: var(--clr-text2);
}

.split-row-inline strong { color: var(--clr-accent); }

/* ---- Note box ---- */
.note-box {
  margin-top: 10px;
  padding: 8px 14px;
  background: rgba(245,158,11,0.07);
  border: 1px solid rgba(245,158,11,0.2);
  border-radius: 6px;
  font-size: 13px;
  color: var(--clr-k1);
}

/* ---- Footer ---- */
.site-footer {
  text-align: center;
  padding: 40px 0 20px;
  color: var(--clr-muted);
  font-size: 13px;
  border-top: 1px solid var(--clr-border);
  margin-top: 40px;
}

.site-footer a { color: var(--clr-accent); text-decoration: none; }

/* ---- Algorithm Reference ---- */
.reference-card {
  background: var(--clr-card);
  border: 1px solid var(--clr-border);
  border-radius: var(--radius);
  padding: 24px 28px;
  margin-bottom: 24px;
}

.ref-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(160px, 1fr));
  gap: 12px;
}

.ref-item {
  background: var(--clr-bg);
  border: 1px solid var(--clr-border);
  border-radius: var(--radius-sm);
  padding: 12px;
}

.ref-name {
  font-size: 11px;
  color: var(--clr-accent);
  font-weight: 600;
  letter-spacing: 0.06em;
  margin-bottom: 4px;
}

.ref-table {
  font-family: var(--font-mono);
  font-size: 12px;
  color: var(--clr-text2);
  word-break: break-all;
}

/* ---- Info chips ---- */
.info-chips {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
  margin-bottom: 24px;
}

.chip {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 5px 14px;
  border-radius: 100px;
  font-size: 12px;
  font-weight: 500;
  border: 1px solid;
}

.chip-cyan { background: rgba(0,245,212,0.06); border-color: rgba(0,245,212,0.2); color: var(--clr-accent); }
.chip-violet { background: rgba(124,58,237,0.08); border-color: rgba(124,58,237,0.25); color: #a78bfa; }
.chip-amber { background: rgba(245,158,11,0.08); border-color: rgba(245,158,11,0.25); color: var(--clr-k1); }

/* ---- Scrollbar ---- */
::-webkit-scrollbar { width: 6px; }
::-webkit-scrollbar-track { background: var(--clr-bg); }
::-webkit-scrollbar-thumb { background: var(--clr-border2); border-radius: 3px; }
::-webkit-scrollbar-thumb:hover { background: var(--clr-accent); }

/* ---- Responsive ---- */
@media (max-width: 640px) {
  .form-grid { grid-template-columns: 1fr; }
  .key-summary { flex-direction: column; }
  .sbox-wrapper { flex-direction: column; }
  .swap-visual { flex-direction: column; gap: 8px; }
  .swap-arrow { transform: rotate(90deg); }
  .step-row { flex-direction: column; align-items: flex-start; }
  .step-label { min-width: unset; }
  .input-card { padding: 20px; }
  .split-visual { flex-direction: column; }
  .split-divider { width: auto; height: 1px; margin: 12px 0; }
  .mode-selector { flex-direction: column; }
  .ref-grid { grid-template-columns: repeat(2, 1fr); }
}

/* ---- Animations ---- */
@keyframes fadeInUp {
  from { opacity: 0; transform: translateY(16px); }
  to   { opacity: 1; transform: translateY(0); }
}

.step-card {
  animation: fadeInUp 0.3s ease both;
}

.step-card:nth-child(2) { animation-delay: 0.05s; }
.step-card:nth-child(3) { animation-delay: 0.10s; }
.step-card:nth-child(4) { animation-delay: 0.15s; }
.step-card:nth-child(5) { animation-delay: 0.20s; }