:root {
  color-scheme: light dark;
  --bg: #f7f9fb;
  --card-bg: #ffffff;
  --border: #d0d7de;
  --text: #1f2933;
  --muted: #52606d;
  --accent: #2563eb;
  --accent-bg: rgba(37, 99, 235, 0.16);
  --used-bg: #e0f2fe;
  --unused-bg: #f3f4f6;
  --font-sans: "Noto Sans JP", "Hiragino Kaku Gothic ProN", "游ゴシック体", system-ui, sans-serif;
  --font-mono: "Roboto Mono", "SFMono-Regular", Menlo, Consolas, "Liberation Mono", monospace;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: var(--font-sans);
  background: var(--bg);
  color: var(--text);
  line-height: 1.6;
}

.page-header,
.page-footer {
  padding: 1.5rem 1rem;
  text-align: center;
  background: #0f172a;
  color: #ffffff;
}

.page-header h1 {
  margin: 0 0 0.5rem;
  font-size: 1.8rem;
}

.notice {
  margin: 0;
  font-size: 0.95rem;
}

main {
  max-width: 960px;
  margin: 2rem auto;
  padding: 0 1rem 2rem;
  display: grid;
  gap: 1.5rem;
}

.card {
  background: var(--card-bg);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 1.5rem;
  box-shadow: 0 10px 30px rgba(15, 23, 42, 0.08);
}

.card h2 {
  margin-top: 0;
  font-size: 1.4rem;
}

.form-group {
  display: flex;
  flex-direction: column;
  margin-bottom: 1rem;
}

.form-group label,
fieldset legend {
  font-weight: 600;
  margin-bottom: 0.5rem;
}

textarea {
  resize: vertical;
  min-height: 160px;
  padding: 0.75rem;
  font-size: 1rem;
  border-radius: 8px;
  border: 1px solid var(--border);
  font-family: var(--font-mono);
}

.visibility-control {
  align-items: flex-start;
  gap: 0.75rem;
}

.toggle-visibility-button {
  padding: 0.4rem 0.9rem;
  font-size: 0.95rem;
  border-radius: 6px;
  border: 1px solid var(--border);
  background: var(--unused-bg);
  color: var(--text);
  cursor: pointer;
  transition: background 0.2s ease, border-color 0.2s ease;
}

.toggle-visibility-button:hover,
.toggle-visibility-button:focus {
  background: var(--accent-bg);
  border-color: var(--accent);
}

.masked {
  filter: blur(0.55rem);
  transition: filter 0.2s ease-in-out;
}

.masked::selection {
  background: transparent;
}

textarea:focus,
input:focus,
button:focus {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
}

input[type="number"] {
  padding: 0.5rem;
  font-size: 1rem;
  border-radius: 8px;
  border: 1px solid var(--border);
  width: 120px;
}

.input-hint {
  margin: 0.25rem 0 0;
  font-size: 0.85rem;
  color: var(--muted);
}

.form-row {
  display: flex;
  flex-wrap: wrap;
  gap: 1.5rem;
}

.radio-group {
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
}

.radio-group label {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  font-weight: 500;
}

.result-block + .result-block {
  margin-top: 1.5rem;
}

.copy-row {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  flex-wrap: wrap;
}

.copy-button {
  padding: 0.35rem 0.75rem;
  font-size: 0.95rem;
  border-radius: 6px;
  border: 1px solid var(--accent);
  background: var(--accent);
  color: #ffffff;
  cursor: pointer;
}

.copy-button:hover,
.copy-button:focus {
  background: #1d4ed8;
  border-color: #1d4ed8;
}

.mono-text {
  font-family: var(--font-mono);
  font-size: 0.95rem;
  overflow-wrap: anywhere;
  padding: 0.35rem 0.5rem;
  background: var(--unused-bg);
  border-radius: 6px;
  display: inline-flex;
  align-items: center;
}

.output-meta {
  margin: 0.5rem 0 0;
  color: var(--muted);
}

.output-note {
  margin-left: 0.5rem;
  font-size: 0.85rem;
  color: #be123c;
}

.split-display {
  margin-top: 0.75rem;
  font-family: var(--font-mono);
  display: flex;
  flex-wrap: wrap;
  gap: 0.15rem;
}

.split-segment {
  padding: 0.25rem 0.35rem;
  border-radius: 4px;
}

.split-segment.used {
  background: var(--used-bg);
  color: #0c4a6e;
  font-weight: 600;
}

.split-segment.unused {
  background: var(--unused-bg);
  color: var(--muted);
}

.split-list {
  list-style: none;
  padding: 0;
  margin: 0;
  display: grid;
  gap: 0.5rem;
}

.split-list li {
  padding: 0.5rem 0.75rem;
  border-radius: 8px;
  border: 1px solid var(--border);
  background: var(--unused-bg);
  font-family: var(--font-mono);
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 0.75rem;
}

.split-list li.used {
  background: var(--used-bg);
  color: #0c4a6e;
}

.split-label {
  font-size: 0.8rem;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--muted);
}

.hidden {
  display: none !important;
}

@media (max-width: 600px) {
  main {
    margin-top: 1rem;
  }

  textarea {
    min-height: 140px;
  }

  .page-header,
  .page-footer {
    padding: 1.25rem 0.75rem;
  }
}