:root {
  --bg: #0f1420;
  --fg: #e8ecf3;
  --muted: #9aa5b8;
  --accent: #4da3ff;
  --card: #171e2e;
  --border: #263049;
  --radius: 10px;
  color-scheme: dark;
}
/* Explicit light theme (toggle button, persisted in localStorage as data-theme). */
:root[data-theme="light"] {
  --bg: #f4f6fa;
  --fg: #1b2333;
  --muted: #5b6478;
  --accent: #1a73e8;
  --card: #ffffff;
  --border: #dde3ee;
  color-scheme: light;
}
/* No explicit choice saved yet: follow the OS preference for light mode.
   (Dark stays the default above, matching the OS dark preference too.) */
@media (prefers-color-scheme: light) {
  :root:not([data-theme]) {
    --bg: #f4f6fa;
    --fg: #1b2333;
    --muted: #5b6478;
    --accent: #1a73e8;
    --card: #ffffff;
    --border: #dde3ee;
    color-scheme: light;
  }
}

/* SVG schematics/plots hardcode dark-theme colors in their markup; remap the
   common ones so they stay readable when the page renders light. */
:root[data-theme="light"] .calc-schematic svg [stroke="#e8ecf3"],
:root[data-theme="light"] .calc-schematic svg [fill="#e8ecf3"],
:root[data-theme="light"] .freq-plot svg [stroke="#e8ecf3"],
:root[data-theme="light"] .freq-plot svg [fill="#e8ecf3"],
:root[data-theme="light"] .symbol-card svg [stroke="#e8ecf3"],
:root[data-theme="light"] .symbol-card svg [fill="#e8ecf3"] {
  stroke: #1b2333 !important;
  fill: #1b2333 !important;
}
:root[data-theme="light"] .calc-schematic svg [stroke="#9aa5b8"],
:root[data-theme="light"] .calc-schematic svg [fill="#9aa5b8"],
:root[data-theme="light"] .freq-plot svg [stroke="#9aa5b8"],
:root[data-theme="light"] .freq-plot svg [fill="#9aa5b8"],
:root[data-theme="light"] .symbol-card svg [stroke="#9aa5b8"],
:root[data-theme="light"] .symbol-card svg [fill="#9aa5b8"] {
  stroke: #5b6478 !important;
  fill: #5b6478 !important;
}
:root[data-theme="light"] .calc-schematic svg [stroke="#263049"],
:root[data-theme="light"] .calc-schematic svg [fill="#263049"],
:root[data-theme="light"] .freq-plot svg [stroke="#263049"],
:root[data-theme="light"] .freq-plot svg [fill="#263049"],
:root[data-theme="light"] .symbol-card svg [stroke="#263049"],
:root[data-theme="light"] .symbol-card svg [fill="#263049"] {
  stroke: #dde3ee !important;
  fill: #dde3ee !important;
}
:root[data-theme="light"] .calc-schematic svg [stroke="#2a3346"],
:root[data-theme="light"] .calc-schematic svg [fill="#2a3346"],
:root[data-theme="light"] .freq-plot svg [stroke="#2a3346"],
:root[data-theme="light"] .freq-plot svg [fill="#2a3346"],
:root[data-theme="light"] .symbol-card svg [stroke="#2a3346"],
:root[data-theme="light"] .symbol-card svg [fill="#2a3346"] {
  stroke: #ffffff !important;
  fill: #ffffff !important;
}
:root[data-theme="light"] .calc-schematic svg [stroke="#1c2437"],
:root[data-theme="light"] .calc-schematic svg [fill="#1c2437"],
:root[data-theme="light"] .freq-plot svg [stroke="#1c2437"],
:root[data-theme="light"] .freq-plot svg [fill="#1c2437"],
:root[data-theme="light"] .symbol-card svg [stroke="#1c2437"],
:root[data-theme="light"] .symbol-card svg [fill="#1c2437"],
:root[data-theme="light"] .calc-schematic svg [stroke="#101827"],
:root[data-theme="light"] .calc-schematic svg [fill="#101827"],
:root[data-theme="light"] .freq-plot svg [stroke="#101827"],
:root[data-theme="light"] .freq-plot svg [fill="#101827"],
:root[data-theme="light"] .symbol-card svg [stroke="#101827"],
:root[data-theme="light"] .symbol-card svg [fill="#101827"],
:root[data-theme="light"] .calc-schematic svg [stroke="#c0c8d4"],
:root[data-theme="light"] .calc-schematic svg [fill="#c0c8d4"],
:root[data-theme="light"] .freq-plot svg [stroke="#c0c8d4"],
:root[data-theme="light"] .freq-plot svg [fill="#c0c8d4"],
:root[data-theme="light"] .symbol-card svg [stroke="#c0c8d4"],
:root[data-theme="light"] .symbol-card svg [fill="#c0c8d4"] {
  stroke: #dde3ee !important;
  fill: #dde3ee !important;
}
* { box-sizing: border-box; }
body {
  margin: 0;
  font-family: system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
  background: var(--bg);
  color: var(--fg);
  line-height: 1.55;
  transition: background-color .15s ease, color .15s ease;
}
.container { max-width: 1200px; margin: 0 auto; padding: 0 20px; }
a { color: var(--accent); text-decoration: none; }
a:hover { text-decoration: underline; }

.site-header {
  border-bottom: 1px solid var(--border);
  background: var(--card);
}
.site-header .container {
  display: flex; align-items: center; justify-content: space-between; height: 60px;
}
.brand { font-weight: 700; font-size: 1.1rem; color: var(--fg); }
.site-header nav a { margin-left: 18px; color: var(--muted); }

.hero { padding: 48px 0 24px; }
.hero h1 { margin: 0 0 8px; font-size: 2rem; }
.hero p { color: var(--muted); margin: 0; font-size: 1.1rem; }

#tools .tools-cat {
  margin: 36px 0 4px;
  font-size: .78rem;
  text-transform: uppercase;
  letter-spacing: .12em;
  color: var(--accent);
  border-bottom: 1px solid var(--border);
  padding-bottom: 8px;
}
#tools .tools-cat:first-child { margin: 28px 0 4px; }
#tools .tool-grid { margin: 16px 0 8px; }
.tool-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(260px, 1fr));
  gap: 16px;
  margin: 20px 0 40px;
}
.tool-card {
  display: block;
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 18px;
  color: var(--fg);
  transition: border-color .15s, transform .15s;
}
.tool-card:hover { border-color: var(--accent); transform: translateY(-2px); text-decoration: none; }
.tool-card h3 { margin: 0 0 6px; font-size: 1.02rem; }
.tool-card p { margin: 0; color: var(--muted); font-size: .9rem; }

/* calculator page */
.tool-page h1 { margin: 32px 0 4px; }
.tool-page .lead { color: var(--muted); margin: 0 0 24px; }

/* 2-column calculator layout: schematic+plot | values (nav moved to header) */
.calc-layout {
  display: grid;
  grid-template-columns: 1fr 280px;
  gap: 16px;
  align-items: start;
  margin-bottom: 24px;
}

/* top header dropdown */
.top-nav { display: flex; align-items: center; gap: 18px; }
.top-dd { position: relative; }
.top-dd summary {
  list-style: none;
  cursor: pointer;
  color: var(--muted);
  font-weight: 600;
  user-select: none;
}
.top-dd summary::-webkit-details-marker { display: none; }
.top-dd summary::after { content: ' ▾'; font-size: .8em; }
.top-dd[open] summary { color: var(--fg); }
.top-dd summary:hover { color: var(--fg); }
.top-dd-panel {
  position: absolute;
  top: calc(100% + 10px);
  right: 0;
  width: 340px;
  max-height: 70vh;
  overflow-y: auto;
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 14px;
  z-index: 300;
  box-shadow: 0 12px 32px rgba(0,0,0,.5);
  display: flex;
  flex-direction: column;
}
.tdd-cat {
  margin: 12px 0 4px;
  font-size: .68rem;
  text-transform: uppercase;
  letter-spacing: .12em;
  color: var(--accent);
}
.tdd-cat:first-child { margin-top: 0; }
.top-dd-panel a {
  color: var(--muted);
  font-size: .92rem;
  padding: 5px 8px;
  border-radius: 6px;
}
.top-dd-panel a:hover { color: var(--fg); background: var(--bg); text-decoration: none; }
.top-link { color: var(--muted); font-weight: 600; }
.top-link:hover { color: var(--fg); }
.site-header .container { gap: 20px; }

/* dark/light theme toggle button */
.theme-toggle {
  background: var(--bg);
  color: var(--fg);
  border: 1px solid var(--border);
  border-radius: 6px;
  padding: 6px 11px;
  font-size: 1rem;
  line-height: 1;
  cursor: pointer;
}
.theme-toggle:hover { border-color: var(--accent); }

/* homepage search/filter box */
#tool-search {
  display: block;
  width: 100%;
  max-width: 420px;
  margin: 16px 0 4px;
  padding: 10px 14px;
  background: var(--card);
  color: var(--fg);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  font-size: 1rem;
}
#tool-search:focus { outline: none; border-color: var(--accent); }
.calc-panel {
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 18px;
}
.calc-panel h3 {
  margin: 0 0 12px;
  font-size: .72rem;
  text-transform: uppercase;
  letter-spacing: .1em;
  color: var(--muted);
}
.calc-schematic {
  display: flex;
  align-items: center;
  justify-content: center;
  min-height: 260px;
}
.calc-schematic svg {
  width: 100%;
  max-width: 420px;
  height: auto;
}
@media (max-width: 900px) {
  .calc-layout { grid-template-columns: 1fr; }
  .calc-layout .calc-nav {
    position: static !important;
    max-height: none !important;
    overflow: visible !important;
  }
}

/* middle column: schematic stacked with plot-like panels directly below */
.calc-mid {
  display: flex;
  flex-direction: column;
  gap: 16px;
}
.calc-mid .freq-plot svg {
  width: 100%;
  height: auto;
}

/* hint text */
.hint { color: var(--muted); font-size: .85em; margin: 6px 0 0; }

/* nav: sticky, scrollable, collapsible category groups */
.calc-nav {
  position: sticky;
  top: 16px;
  max-height: calc(100vh - 32px);
  overflow-y: auto;
}
.calc-nav nav {
  display: flex;
  flex-direction: column;
}
.calc-nav details { margin-top: 14px; }
.calc-nav details:first-of-type { margin-top: 0; }
.calc-nav summary {
  cursor: pointer;
  list-style: none;
  display: flex;
  align-items: center;
  gap: 6px;
  font-size: .68rem;
  text-transform: uppercase;
  letter-spacing: .12em;
  color: var(--muted);
  user-select: none;
}
.calc-nav summary::-webkit-details-marker { display: none; }
.calc-nav summary::before { content: '▸'; font-size: .7rem; transition: transform .15s; }
.calc-nav details[open] > summary::before { transform: rotate(90deg); }
.calc-nav summary:hover { color: var(--fg); }
.calc-nav .nav-group {
  display: flex;
  flex-direction: column;
  gap: 2px;
  margin-top: 6px;
}
.calc-nav nav a:not(.active):hover { color: var(--accent); }
.calc-nav nav a.active {
  color: var(--accent);
  background: var(--bg);
  border-color: var(--accent);
  font-weight: 600;
}

/* preset example buttons */
.presets { display: flex; flex-wrap: wrap; gap: 6px; margin: 10px 0 4px; }
.preset {
  background: var(--bg); color: var(--accent);
  border: 1px solid var(--border); border-radius: 6px;
  padding: 4px 10px; font-size: .82rem; cursor: pointer;
}
.preset:hover { border-color: var(--accent); }

/* copy-result button */
.copy-btn {
  display: block; margin-top: 10px;
  background: var(--bg); color: var(--accent);
  border: 1px solid var(--border); border-radius: 6px;
  padding: 5px 12px; font-size: .85rem; cursor: pointer;
}
.copy-btn:hover { border-color: var(--accent); }

/* related calculators section */
.related { margin-top: 44px; }
.related h2 { font-size: 1.15rem; }
.related .tool-grid { margin-top: 14px; }

/* component symbols reference */
.sym-intro { color: var(--muted); margin: 4px 0 8px; }
.sym-cat {
  margin: 40px 0 14px;
  font-size: 1.05rem;
  color: var(--accent);
  border-bottom: 1px solid var(--border);
  padding-bottom: 8px;
}
.symbol-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(230px, 1fr));
  gap: 16px;
}
.symbol-card {
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 16px;
  display: flex;
  flex-direction: column;
  align-items: center;
  text-align: center;
}
.symbol-card svg {
  width: 100%;
  max-width: 240px;
  height: auto;
  background: var(--bg);
  border-radius: 8px;
  padding: 4px;
  margin-bottom: 10px;
}
.symbol-card h3 { margin: 0 0 4px; font-size: 1rem; }
.symbol-card .sym-what { margin: 0; font-size: .9rem; }
.symbol-card .sym-use { margin: 4px 0 0; color: var(--muted); font-size: .85rem; }
.symbol-card .sym-link { margin-top: 10px; font-size: .85rem; }

.calc label { display: block; margin: 12px 0 4px; font-weight: 600; font-size: .92rem; }
.calc input[type="number"], .calc select {
  width: 100%; padding: 9px 11px;
  background: var(--bg); color: var(--fg);
  border: 1px solid var(--border); border-radius: 7px;
  font-size: 1rem;
}
.calc-panel .result {
  margin-top: 4px; padding: 14px;
  background: var(--bg); border: 1px solid var(--border);
  border-radius: 7px; font-size: 1.05rem;
}
.calc-panel .result strong { color: var(--accent); }
.muted { color: var(--muted); font-size: .85em; }
.explanation { color: var(--muted); }
.explanation h2 { color: var(--fg); font-size: 1.15rem; }

.site-footer {
  border-top: 1px solid var(--border);
  margin-top: 60px; padding: 20px 0;
  color: var(--muted); font-size: .88rem;
}
.site-footer .container { display: flex; justify-content: space-between; align-items: center; flex-wrap: wrap; gap: 8px; }
.site-footer nav a { margin-left: 16px; color: var(--muted); }

@media (max-width: 600px) {
  .hero { padding: 28px 0 12px; }
  .hero h1 { font-size: 1.5rem; }
}