/* ===== Reset & Base ===== */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

:root {
  --bg-primary: #0f1117;
  --bg-secondary: #1a1d27;
  --bg-card: #212433;
  --bg-input: #161921;
  --border: #2a2d3a;
  --text-primary: #e4e6f0;
  --text-secondary: #8b8fa3;
  --text-muted: #5c6072;
  --accent: #4a9eff;
  --accent-hover: #3d8ae6;
  --accent-glow: rgba(74, 158, 255, 0.15);
  --green: #34d399;
  --orange: #fb923c;
  --red: #f87171;
  --purple: #a78bfa;
  --yellow: #fbbf24;
  --radius: 10px;
  --radius-sm: 6px;
  --transition: 0.2s ease;
}

html { font-size: 16px; scroll-behavior: smooth; }

body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC",
    "Microsoft YaHei", "Helvetica Neue", sans-serif;
  background: var(--bg-primary);
  color: var(--text-primary);
  display: grid;
  grid-template-columns: 260px 1fr;
  grid-template-rows: auto 1fr auto;
  grid-template-areas:
    "header header"
    "sidebar main"
    "footer footer";
  min-height: 100vh;
}

/* ===== Header ===== */
.header {
  grid-area: header;
  background: var(--bg-secondary);
  border-bottom: 1px solid var(--border);
  padding: 18px 28px;
}
.header-inner { display: flex; align-items: baseline; gap: 16px; flex-wrap: wrap; }
.logo { font-size: 1.4rem; font-weight: 700; color: var(--text-primary); }
.subtitle { font-size: 0.875rem; color: var(--text-secondary); }

/* ===== Sidebar ===== */
.sidebar {
  grid-area: sidebar;
  background: var(--bg-secondary);
  border-right: 1px solid var(--border);
  padding: 16px 0;
  display: flex;
  flex-direction: column;
  overflow-y: auto;
}
.sidebar-title {
  font-size: 0.75rem;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--text-muted);
  padding: 4px 20px 12px;
}
.tool-nav { list-style: none; flex: 1; }
.tool-btn {
  display: block;
  width: 100%;
  text-align: left;
  padding: 10px 20px;
  border: none;
  background: transparent;
  color: var(--text-secondary);
  font-size: 0.9rem;
  cursor: pointer;
  transition: var(--transition);
  border-left: 3px solid transparent;
  font-family: inherit;
}
.tool-btn:hover { background: var(--bg-card); color: var(--text-primary); }
.tool-btn.active {
  background: var(--accent-glow);
  color: var(--accent);
  border-left-color: var(--accent);
  font-weight: 600;
}
.sidebar-footer { padding: 12px 20px; border-top: 1px solid var(--border); }
.github-link {
  color: var(--text-muted);
  text-decoration: none;
  font-size: 0.85rem;
  transition: var(--transition);
}
.github-link:hover { color: var(--text-primary); }

/* ===== Main Content ===== */
.main-content {
  grid-area: main;
  padding: 28px 32px;
  overflow-y: auto;
}

/* ===== Tool Panel ===== */
.tool-panel { display: none; }
.tool-panel.active { display: block; }

.tool-header { margin-bottom: 24px; }
.tool-header h2 { font-size: 1.5rem; margin-bottom: 6px; }
.tool-header p { color: var(--text-secondary); font-size: 0.9rem; }

.tool-body {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 24px;
}

/* ===== Form Elements ===== */
.form-group { margin-bottom: 16px; }
.form-group:last-child { margin-bottom: 0; }
.form-label {
  display: block;
  font-size: 0.85rem;
  color: var(--text-secondary);
  margin-bottom: 6px;
  font-weight: 500;
}
.form-row {
  display: flex;
  gap: 12px;
  align-items: center;
}
.form-input {
  flex: 1;
  background: var(--bg-input);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  padding: 10px 14px;
  color: var(--text-primary);
  font-size: 0.95rem;
  font-family: "SF Mono", "Fira Code", "Consolas", monospace;
  transition: var(--transition);
  min-width: 0;
}
.form-input:focus {
  outline: none;
  border-color: var(--accent);
  box-shadow: 0 0 0 3px var(--accent-glow);
}
.form-input::placeholder { color: var(--text-muted); }
.form-select {
  background: var(--bg-input);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  padding: 10px 32px 10px 12px;
  color: var(--text-primary);
  font-size: 0.9rem;
  cursor: pointer;
  appearance: none;
  background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='12' height='12' viewBox='0 0 12 12'%3E%3Cpath fill='%238b8fa3' d='M6 8L1 3h10z'/%3E%3C/svg%3E");
  background-repeat: no-repeat;
  background-position: right 10px center;
  font-family: inherit;
}
.form-select:focus { outline: none; border-color: var(--accent); }

.btn {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 10px 20px;
  border: none;
  border-radius: var(--radius-sm);
  font-size: 0.9rem;
  font-weight: 600;
  cursor: pointer;
  transition: var(--transition);
  font-family: inherit;
}
.btn-primary { background: var(--accent); color: #fff; }
.btn-primary:hover { background: var(--accent-hover); }
.btn-secondary {
  background: transparent;
  border: 1px solid var(--border);
  color: var(--text-secondary);
}
.btn-secondary:hover { border-color: var(--text-muted); color: var(--text-primary); }

/* ===== Results ===== */
.result-box {
  margin-top: 20px;
  padding: 16px;
  background: var(--bg-input);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
}
.result-label {
  font-size: 0.8rem;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-bottom: 8px;
}
.result-value {
  font-family: "SF Mono", "Fira Code", "Consolas", monospace;
  font-size: 1.1rem;
  color: var(--accent);
  word-break: break-all;
}

.result-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(180px, 1fr));
  gap: 10px;
  margin-top: 16px;
}
.result-item {
  background: var(--bg-input);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  padding: 12px;
  text-align: center;
}
.result-item .unit { font-size: 0.75rem; color: var(--text-muted); margin-bottom: 4px; }
.result-item .value {
  font-family: "SF Mono", "Fira Code", "Consolas", monospace;
  font-size: 1.05rem;
  color: var(--text-primary);
  word-break: break-all;
}
.result-item.highlight {
  border-color: var(--accent);
  background: var(--accent-glow);
}
.result-item.highlight .value { color: var(--accent); font-weight: 700; }

/* ===== Color Code ===== */
.color-bands { display: flex; gap: 12px; flex-wrap: wrap; margin: 16px 0; align-items: flex-end; }
.band-group { display: flex; flex-direction: column; align-items: center; gap: 6px; }
.band-label { font-size: 0.75rem; color: var(--text-muted); }
.band-color {
  width: 36px;
  height: 36px;
  border-radius: 50%;
  border: 2px solid var(--border);
  cursor: pointer;
  transition: var(--transition);
}
.band-color:hover { border-color: var(--accent); transform: scale(1.1); }
.band-color.band-active {
  border-color: var(--accent);
  box-shadow: 0 0 10px var(--accent-glow);
  transform: scale(1.15);
}
.band-select {
  background: var(--bg-input);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  color: var(--text-primary);
  padding: 4px 8px;
  font-size: 0.8rem;
  cursor: pointer;
  max-width: 100px;
  font-family: inherit;
}

.color-options {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(48px, 1fr));
  gap: 6px;
  margin-top: 12px;
  padding: 12px;
  background: var(--bg-input);
  border-radius: var(--radius-sm);
  border: 1px solid var(--border);
}
.color-swatch {
  width: 100%;
  aspect-ratio: 1;
  border-radius: 50%;
  border: 2px solid transparent;
  cursor: pointer;
  transition: var(--transition);
}
.color-swatch:hover { border-color: #fff; transform: scale(1.2); }
.color-swatch.swatch-selected {
  border-color: var(--accent);
  box-shadow: 0 0 8px var(--accent-glow);
  transform: scale(1.15);
}

/* ===== Ohm's Law Triangle ===== */
.ohms-triangle {
  display: flex;
  justify-content: center;
  margin: 20px 0;
}
.triangle-grid {
  display: grid;
  grid-template-columns: repeat(3, 90px);
  grid-template-rows: auto auto;
  gap: 4px;
  text-align: center;
}
.tri-v {
  grid-column: 1 / -1;
  background: var(--accent);
  color: #fff;
  padding: 10px;
  border-radius: var(--radius-sm) var(--radius-sm) 0 0;
  font-weight: 700;
  font-size: 1.2rem;
}
.tri-i, .tri-r {
  background: var(--bg-input);
  border: 1px solid var(--border);
  padding: 10px;
  font-family: "SF Mono", "Fira Code", "Consolas", monospace;
  font-size: 0.9rem;
  color: var(--text-secondary);
}
.tri-i { border-radius: 0 0 0 var(--radius-sm); }
.tri-r { border-radius: 0 0 var(--radius-sm) 0; }
.tri-plus { background: transparent; color: var(--text-muted); }

.formula-box {
  background: var(--bg-input);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  padding: 10px 16px;
  font-family: "SF Mono", "Fira Code", "Consolas", monospace;
  font-size: 0.85rem;
  color: var(--text-secondary);
  margin-top: 12px;
  text-align: center;
}

/* ===== Quantity Tabs ===== */
.quantity-tabs {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
}
.quantity-tab {
  padding: 8px 16px;
  border: 1px solid var(--border);
  border-radius: 20px;
  background: transparent;
  color: var(--text-secondary);
  font-size: 0.85rem;
  cursor: pointer;
  transition: var(--transition);
  font-family: inherit;
  white-space: nowrap;
}
.quantity-tab:hover {
  border-color: var(--text-muted);
  color: var(--text-primary);
}
.quantity-tab.active {
  background: var(--accent);
  border-color: var(--accent);
  color: #fff;
  font-weight: 600;
}

/* ===== Footer ===== */
.footer {
  grid-area: footer;
  background: var(--bg-secondary);
  border-top: 1px solid var(--border);
  padding: 12px 28px;
  text-align: center;
  font-size: 0.8rem;
  color: var(--text-muted);
}

/* ===== Mobile ===== */
@media (max-width: 768px) {
  body {
    grid-template-columns: 1fr;
    grid-template-rows: auto auto 1fr auto;
    grid-template-areas:
      "header"
      "sidebar"
      "main"
      "footer";
  }
  .sidebar {
    flex-direction: row;
    overflow-x: auto;
    padding: 8px 12px;
    border-right: none;
    border-bottom: 1px solid var(--border);
  }
  .sidebar-title { display: none; }
  .tool-nav { display: flex; gap: 4px; flex: none; }
  .tool-btn {
    white-space: nowrap;
    font-size: 0.8rem;
    padding: 6px 14px;
    border-left: none;
    border-radius: 20px;
  }
  .tool-btn.active { border-left: none; }
  .sidebar-footer { display: none; }
  .main-content { padding: 16px; }
  .result-grid { grid-template-columns: repeat(auto-fill, minmax(140px, 1fr)); }
}

/* ===== Color Code Resistor Visual ===== */
.resistor-visual {
  display: flex;
  align-items: center;
  justify-content: center;
  margin: 20px 0;
  gap: 0;
}
.resistor-body {
  width: 200px;
  height: 48px;
  background: #e8d5b7;
  border-radius: 6px;
  position: relative;
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 16px;
}
.resistor-lead {
  width: 40px;
  height: 3px;
  background: #c0c0c0;
}
.band {
  width: 12px;
  height: 40px;
  border-radius: 2px;
}

/* Swatch hint */
.swatch-label {
  font-size: 0.7rem;
  color: var(--text-muted);
  text-align: center;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}