/* =============================================
   S-DES Simulator — Clean Academic Theme
   ============================================= */

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

:root {
  --ink:       #1a1a2e;
  --ink-light: #3d3d5c;
  --ink-muted: #7a7a9a;
  --paper:     #f7f7f9;
  --white:     #ffffff;
  --blue:      #2563eb;
  --blue-dim:  #dbeafe;
  --green:     #16a34a;
  --green-dim: #dcfce7;
  --red:       #dc2626;
  --border:    #e2e2ec;
  --shadow:    0 1px 4px rgba(0,0,0,0.07), 0 4px 16px rgba(0,0,0,0.05);
  --mono: 'IBM Plex Mono', monospace;
  --sans: 'IBM Plex Sans', sans-serif;
}

body {
  font-family: var(--sans);
  background: var(--paper);
  color: var(--ink);
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

/* ---- HEADER ---- */
header {
  background: var(--white);
  border-bottom: 2px solid var(--ink);
  padding: 18px 0;
  position: sticky;
  top: 0;
  z-index: 10;
}
.header-inner {
  max-width: 860px;
  margin: 0 auto;
  padding: 0 24px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
}
.header-left {
  display: flex;
  align-items: center;
  gap: 14px;
}
.header-badge {
  background: var(--ink);
  color: var(--white);
  font-family: var(--mono);
  font-size: 13px;
  font-weight: 600;
  letter-spacing: 0.08em;
  padding: 5px 10px;
  border-radius: 4px;
  flex-shrink: 0;
}
header h1 {
  font-size: 18px;
  font-weight: 700;
  line-height: 1.2;
  color: var(--ink);
}
header p {
  font-size: 12px;
  color: var(--ink-muted);
  margin-top: 2px;
}
.header-right {
  font-family: var(--mono);
  font-size: 11px;
  color: var(--ink-muted);
  white-space: nowrap;
}

/* ---- MAIN ---- */
main {
  max-width: 860px;
  margin: 0 auto;
  padding: 32px 24px;
  flex: 1;
  display: flex;
  flex-direction: column;
  gap: 24px;
}

.card {
  background: var(--white);
  border: 1.5px solid var(--border);
  border-radius: 10px;
  padding: 28px 32px;
  box-shadow: var(--shadow);
}

.section-title {
  font-size: 13px;
  font-weight: 600;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--ink-muted);
  margin-bottom: 22px;
  padding-bottom: 10px;
  border-bottom: 1px solid var(--border);
}

/* ---- FORM ---- */
.field-group {
  margin-bottom: 20px;
}
.field-group label {
  display: block;
  font-size: 14px;
  font-weight: 600;
  margin-bottom: 7px;
  color: var(--ink);
}
.hint {
  font-weight: 400;
  font-family: var(--mono);
  font-size: 12px;
  color: var(--ink-muted);
}
.field-group input[type="text"] {
  width: 100%;
  font-family: var(--mono);
  font-size: 18px;
  letter-spacing: 0.18em;
  padding: 11px 14px;
  border: 1.5px solid var(--border);
  border-radius: 6px;
  background: var(--paper);
  color: var(--ink);
  outline: none;
  transition: border-color 0.15s;
}
.field-group input[type="text"]:focus {
  border-color: var(--blue);
  background: var(--white);
}
.field-note {
  display: block;
  font-size: 12px;
  margin-top: 5px;
  color: var(--red);
  font-family: var(--mono);
  min-height: 16px;
}
.field-note.ok { color: var(--green); }

.mode-toggle {
  display: flex;
  gap: 8px;
}
.mode-btn {
  font-family: var(--sans);
  font-size: 14px;
  font-weight: 500;
  padding: 9px 24px;
  border: 1.5px solid var(--border);
  border-radius: 6px;
  background: var(--paper);
  color: var(--ink-light);
  cursor: pointer;
  transition: all 0.12s;
}
.mode-btn.active {
  background: var(--ink);
  color: var(--white);
  border-color: var(--ink);
}
.mode-btn:not(.active):hover {
  border-color: var(--ink-light);
  color: var(--ink);
}

.btn-row {
  display: flex;
  gap: 10px;
  margin-top: 6px;
}
.btn-submit, .btn-reset {
  font-family: var(--sans);
  font-size: 14px;
  font-weight: 600;
  padding: 11px 28px;
  border-radius: 6px;
  cursor: pointer;
  border: 1.5px solid transparent;
  transition: all 0.12s;
}
.btn-submit {
  background: var(--blue);
  color: var(--white);
  border-color: var(--blue);
}
.btn-submit:hover { background: #1d4ed8; }
.btn-reset {
  background: var(--white);
  color: var(--ink-light);
  border-color: var(--border);
}
.btn-reset:hover { border-color: var(--ink-light); color: var(--ink); }

/* ---- RESULT ---- */
.result-display {
  background: var(--paper);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 20px 22px;
  margin-bottom: 20px;
}
.result-label {
  display: block;
  font-size: 12px;
  font-weight: 600;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--ink-muted);
  margin-bottom: 12px;
}
.bit-row {
  display: flex;
  gap: 6px;
  flex-wrap: wrap;
}
.bit-cell {
  width: 38px;
  height: 38px;
  border-radius: 5px;
  border: 1.5px solid var(--border);
  background: var(--white);
  display: flex;
  align-items: center;
  justify-content: center;
  font-family: var(--mono);
  font-size: 18px;
  font-weight: 600;
  color: var(--ink);
  position: relative;
}
.bit-cell.one {
  background: var(--ink);
  color: var(--white);
  border-color: var(--ink);
}
.bit-cell .pos {
  position: absolute;
  bottom: 2px;
  right: 3px;
  font-size: 8px;
  font-family: var(--mono);
  color: var(--ink-muted);
  opacity: 0.6;
}
.bit-cell.one .pos { color: #aaa; }

/* ---- TOGGLE STEPS ---- */
.toggle-steps-row { text-align: center; }
.toggle-steps-btn {
  background: none;
  border: 1.5px solid var(--border);
  border-radius: 6px;
  padding: 9px 20px;
  font-family: var(--sans);
  font-size: 13px;
  font-weight: 500;
  color: var(--ink-light);
  cursor: pointer;
  transition: all 0.12s;
}
.toggle-steps-btn:hover { border-color: var(--ink-light); color: var(--ink); }

/* ---- STEPS PANEL ---- */
.steps-panel {
  margin-top: 24px;
  border-top: 1px solid var(--border);
  padding-top: 24px;
}

/* ---- STEP BLOCKS ---- */
.step-group {
  margin-bottom: 28px;
}
.step-group-title {
  font-size: 12px;
  font-weight: 700;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--blue);
  margin-bottom: 14px;
  display: flex;
  align-items: center;
  gap: 8px;
}
.step-group-title::after {
  content: '';
  flex: 1;
  height: 1px;
  background: var(--blue-dim);
}

.step-block {
  background: var(--paper);
  border: 1px solid var(--border);
  border-left: 3px solid var(--border);
  border-radius: 0 6px 6px 0;
  padding: 14px 16px;
  margin-bottom: 10px;
}
.step-block.highlight {
  border-left-color: var(--blue);
  background: var(--blue-dim);
}
.step-block.success {
  border-left-color: var(--green);
  background: var(--green-dim);
}

.step-label {
  font-size: 11px;
  font-weight: 700;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  color: var(--ink-muted);
  margin-bottom: 8px;
}
.step-block.highlight .step-label { color: var(--blue); }
.step-block.success .step-label { color: var(--green); }

.step-bits {
  display: flex;
  flex-wrap: wrap;
  gap: 4px;
  align-items: center;
}
.step-bit {
  width: 28px;
  height: 28px;
  border-radius: 4px;
  border: 1px solid #ccc;
  background: var(--white);
  display: flex;
  align-items: center;
  justify-content: center;
  font-family: var(--mono);
  font-size: 13px;
  font-weight: 600;
  color: var(--ink);
}
.step-bit.one {
  background: var(--ink);
  color: var(--white);
  border-color: var(--ink);
}
.step-bit.blue-one {
  background: var(--blue);
  color: var(--white);
  border-color: var(--blue);
}
.step-sep {
  font-family: var(--mono);
  font-size: 13px;
  color: var(--ink-muted);
  padding: 0 4px;
}
.step-arrow {
  color: var(--ink-muted);
  font-size: 12px;
  margin: 0 4px;
}

.sub-row {
  display: flex;
  flex-wrap: wrap;
  gap: 16px;
  margin-top: 6px;
}
.sub-col { flex: 1; min-width: 120px; }
.sub-label {
  font-size: 11px;
  font-weight: 600;
  color: var(--ink-muted);
  margin-bottom: 5px;
  font-family: var(--mono);
}

.sbox-table {
  border-collapse: collapse;
  font-family: var(--mono);
  font-size: 12px;
  margin-top: 8px;
}
.sbox-table td, .sbox-table th {
  border: 1px solid var(--border);
  padding: 4px 8px;
  text-align: center;
}
.sbox-table th {
  background: var(--paper);
  font-size: 11px;
  color: var(--ink-muted);
}
.sbox-table .highlight-cell {
  background: var(--blue);
  color: white;
  font-weight: 700;
}

/* ---- FOOTER ---- */
footer {
  border-top: 1px solid var(--border);
  padding: 16px 24px;
  text-align: center;
  font-size: 12px;
  color: var(--ink-muted);
}

/* ---- RESPONSIVE ---- */
@media (max-width: 600px) {
  .header-right { display: none; }
  .card { padding: 20px 16px; }
  header h1 { font-size: 15px; }
  .bit-cell { width: 32px; height: 32px; font-size: 15px; }
  .step-bit { width: 24px; height: 24px; font-size: 11px; }
  .field-group input[type="text"] { font-size: 15px; }
}