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

:root {
  --bg: #0f1117;
  --surface: #1a1d27;
  --border: #2a2e3d;
  --text: #e4e6ef;
  --text-muted: #7a7f94;
  --accent: #6c8cff;
  --bit-on: #6c8cff;
  --bit-off: #3a3e50;
  --radius: 6px;
  --font-mono: "SF Mono", "Fira Code", "JetBrains Mono", "Cascadia Code", monospace;
  --font-sans: "Inter", -apple-system, BlinkMacSystemFont, "Segoe UI", system-ui, sans-serif;
}

html {
  font-size: 16px;
  -webkit-font-smoothing: antialiased;
}

body {
  font-family: var(--font-sans);
  background: var(--bg);
  color: var(--text);
  min-height: 100vh;
  display: flex;
  justify-content: center;
  padding: 3rem 1.5rem;
}

main {
  width: 100%;
  max-width: 720px;
}

.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border-width: 0;
}

/* Header */

header {
  text-align: center;
  margin-bottom: 2.5rem;
  position: relative;
}

.github-link {
  position: absolute;
  top: 0;
  right: 0;
  color: var(--text-muted);
  transition: color 0.2s;
}

.github-link:hover {
  color: var(--text);
}

h1 {
  font-family: var(--font-mono);
  font-size: 2rem;
  font-weight: 700;
  letter-spacing: -0.02em;
}

.accent {
  color: var(--accent);
}

.subtitle {
  color: var(--text-muted);
  margin-top: 0.5rem;
  font-size: 0.95rem;
}

/* Input */

.input-section {
  display: flex;
  justify-content: center;
  margin-bottom: 2rem;
}

.ip-input-group {
  display: flex;
  align-items: center;
  gap: 0.25rem;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 0.5rem 1rem;
  transition: border-color 0.2s;
}

.ip-input-group:focus-within {
  border-color: var(--accent);
}

.octet-input {
  width: 3.5rem;
  background: transparent;
  border: none;
  outline: none;
  color: var(--text);
  font-family: var(--font-mono);
  font-size: 1.5rem;
  text-align: center;
  padding: 0.35rem 0;
}

.octet-input::placeholder {
  color: var(--text-muted);
  opacity: 0.4;
}

.octet-input.invalid {
  color: #ff6b6b;
}

.dot {
  color: var(--text-muted);
  font-family: var(--font-mono);
  font-size: 1.5rem;
  user-select: none;
}

/* Binary output */

.binary-output {
  text-align: center;
  font-family: var(--font-mono);
  font-size: 1.15rem;
  color: var(--accent);
  min-height: 1.6em;
  letter-spacing: 0.04em;
  margin-bottom: 2.5rem;
  transition: opacity 0.3s;
}

.binary-output:empty {
  opacity: 0;
}

.binary-output .binary-separator {
  color: var(--text-muted);
  margin: 0 0.15em;
}

/* Unified bit table */

.table-section {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.25rem;
  margin-bottom: 1.25rem;
  overflow-x: auto;
}

.bit-table {
  width: 100%;
  border-collapse: collapse;
}

.bit-table th,
.bit-table td {
  text-align: center;
  padding: 0.45rem 0;
  font-family: var(--font-mono);
}

.bit-table thead th {
  font-size: 0.7rem;
  font-weight: 600;
  color: var(--text-muted);
  letter-spacing: 0.04em;
  padding-bottom: 0.3rem;
}

.bit-table .power-row th {
  font-size: 0.6rem;
  font-weight: 400;
  opacity: 0.6;
  padding-bottom: 0.15rem;
}

.bit-table .col-result {
  font-size: 0.6rem;
  text-transform: uppercase;
  letter-spacing: 0.06em;
}

.bit-table tbody tr {
  border-top: 1px solid var(--border);
}

.bit-table tbody td {
  font-size: 1.05rem;
  font-weight: 700;
  transition: color 0.2s;
}

.bit-table td.bit-on {
  color: var(--bit-on);
}

.bit-table td.bit-off {
  color: var(--bit-off);
}

.bit-table .row-label {
  text-align: left;
  font-weight: 400;
  white-space: nowrap;
  padding-right: 0.75rem;
}

.row-label-ordinal {
  font-size: 0.65rem;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: 0.06em;
}

.row-label-value {
  font-size: 1.1rem;
  font-weight: 700;
  color: var(--text);
  margin-left: 0.15rem;
}

.bit-table .row-result {
  font-size: 0.8rem;
  color: var(--accent);
  letter-spacing: 0.04em;
  padding-left: 0.5rem;
  text-align: right;
  white-space: nowrap;
}

/* Step-by-step details */

.steps-section {
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
}

.steps-heading {
  font-size: 0.7rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--text-muted);
  margin-bottom: 0.25rem;
}

.octet-details {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 0 1rem;
  transition: border-color 0.2s;
}

.octet-details:hover {
  border-color: var(--accent);
}

.octet-details[open] {
  padding-bottom: 1rem;
  border-color: var(--accent);
}

.octet-details summary {
  font-family: var(--font-mono);
  font-size: 0.85rem;
  color: var(--text-muted);
  cursor: pointer;
  padding: 0.75rem 0;
  list-style: none;
  display: flex;
  align-items: center;
  gap: 0.5rem;
  user-select: none;
}

.octet-details summary::-webkit-details-marker {
  display: none;
}

.octet-details summary strong {
  color: var(--text);
}

.summary-chevron {
  margin-left: auto;
  display: flex;
  align-items: center;
  transition: transform 0.2s;
}

.octet-details[open] .summary-chevron {
  transform: rotate(90deg);
}

.summary-hint {
  font-size: 0.7rem;
  color: var(--text-muted);
  opacity: 0.6;
  margin-left: auto;
  font-family: var(--font-sans);
}

.octet-details[open] .summary-hint {
  display: none;
}

.steps {
  display: flex;
  flex-direction: column;
  gap: 0.3rem;
  padding-top: 0.25rem;
}

.step {
  font-size: 0.8rem;
  font-family: var(--font-mono);
  color: var(--text-muted);
  line-height: 1.6;
}

.step-value {
  color: var(--text);
}

.step-bit {
  font-weight: 700;
}

.step-bit.on {
  color: var(--bit-on);
}

.step-bit.off {
  color: var(--bit-off);
}

/* Responsive */

@media (max-width: 480px) {
  body {
    padding: 2rem 1rem;
  }

  h1 {
    font-size: 1.5rem;
  }

  .octet-input {
    width: 2.8rem;
    font-size: 1.2rem;
  }

  .dot {
    font-size: 1.2rem;
  }

  .table-section {
    padding: 0.75rem;
  }

  .bit-table thead th {
    font-size: 0.6rem;
  }

  .bit-table tbody td {
    font-size: 0.9rem;
  }

  .row-label-value {
    font-size: 0.9rem;
  }

  .bit-table .row-result {
    font-size: 0.7rem;
  }

  .binary-output {
    font-size: 0.95rem;
  }
}