:root {
  --bg-1: #1f2233;
  --bg-2: #12141f;
  --calc-bg: #262a40;
  --display-bg: #1a1d2b;
  --key-num-bg: #343954;
  --key-num-bg-hover: #3d436180;
  --key-fn-bg: #4a4f70;
  --key-fn-bg-hover: #5a6086;
  --key-op-bg: #ff9f43;
  --key-op-bg-hover: #ffb267;
  --key-eq-bg: #ff5e62;
  --key-eq-bg-hover: #ff7a7d;
  --text-main: #f4f5fb;
  --text-muted: #8b8fae;
  --shadow: rgba(0, 0, 0, 0.35);
  --input-bg: #1a1d2b;
  --border: #3a3f5c;
  --accent: #ff9f43;
  --accent-hover: #ffb267;
  --good: #4ade80;
  --bad: #ff5e62;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  min-height: 100vh;
  display: flex;
  align-items: flex-start;
  justify-content: center;
  background: radial-gradient(circle at top, var(--bg-1), var(--bg-2));
  font-family: "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  padding: 16px;
}

body:has(> .calculator),
body:has(> .page) {
  align-items: center;
}

/* ---------- Shared page chrome ---------- */

.page {
  width: 100%;
  max-width: 640px;
  margin: 0 auto;
  padding: 24px 0 48px;
}

.site-header {
  margin-bottom: 20px;
  text-align: center;
}

.back-link {
  display: inline-block;
  color: var(--text-muted);
  text-decoration: none;
  font-size: 0.9rem;
  margin-bottom: 10px;
  transition: color 0.15s ease;
}

.back-link:hover {
  color: var(--accent);
}

.page-title {
  color: var(--text-main);
  font-size: 1.6rem;
  font-weight: 700;
  margin: 0;
}

.page-subtitle {
  color: var(--text-muted);
  font-size: 0.95rem;
  margin: 8px 0 0;
}

/* ---------- Tool card ---------- */

.tool {
  background: var(--calc-bg);
  border-radius: 20px;
  padding: 24px;
  box-shadow: 0 20px 50px var(--shadow);
}

.tool + .tool,
.calculator + .tool {
  margin-top: 20px;
}

.tool-section-title {
  color: var(--text-main);
  font-size: 1.05rem;
  font-weight: 700;
  margin: 0 0 14px;
}

.tool-hint {
  color: var(--text-muted);
  font-size: 0.85rem;
  margin: -6px 0 16px;
  line-height: 1.4;
}

.about-text {
  color: #ffffff;
  font-size: 0.95rem;
  line-height: 1.65;
  margin: 0 0 14px;
}

.about-text:last-child {
  margin-bottom: 0;
}

/* ---------- Tabs ---------- */

.tabs {
  display: flex;
  gap: 8px;
  margin-bottom: 20px;
  flex-wrap: wrap;
}

.tab {
  flex: 1 1 auto;
  border: none;
  border-radius: 12px;
  padding: 10px 14px;
  background: var(--key-num-bg);
  color: var(--text-muted);
  font-weight: 600;
  font-size: 0.85rem;
  cursor: pointer;
  transition: background 0.15s ease, color 0.15s ease;
  white-space: nowrap;
}

.tab:hover {
  background: var(--key-num-bg-hover);
}

.tab.active {
  background: var(--accent);
  color: #2a1600;
}

.tab-panel {
  display: none;
}

.tab-panel.active {
  display: block;
}

/* ---------- Form fields ---------- */

.field {
  margin-bottom: 16px;
}

.field label {
  display: block;
  color: var(--text-muted);
  font-size: 0.8rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.03em;
  margin-bottom: 6px;
}

.field input,
.field select {
  width: 100%;
  background: var(--input-bg);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 12px 14px;
  color: var(--text-main);
  font-size: 1.05rem;
  font-family: inherit;
  transition: border-color 0.15s ease;
}

.field input:focus,
.field select:focus {
  outline: none;
  border-color: var(--accent);
}

.field-row {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 12px;
}

@media (max-width: 480px) {
  .field-row {
    grid-template-columns: 1fr;
  }
}

/* ---------- Buttons ---------- */

.btn {
  border: none;
  border-radius: 10px;
  padding: 12px 18px;
  font-weight: 700;
  font-size: 0.95rem;
  cursor: pointer;
  transition: background 0.15s ease, transform 0.08s ease;
}

.btn:active {
  transform: scale(0.97);
}

.btn-primary {
  background: var(--accent);
  color: #2a1600;
}

.btn-primary:hover {
  background: var(--accent-hover);
}

.btn-ghost {
  background: var(--key-fn-bg);
  color: var(--text-main);
}

.btn-ghost:hover {
  background: var(--key-fn-bg-hover);
}

.btn-full {
  width: 100%;
}

.btn-remove {
  background: transparent;
  border: 1px solid var(--border);
  color: var(--text-muted);
  border-radius: 8px;
  width: 34px;
  height: 34px;
  flex: 0 0 auto;
  font-size: 1rem;
  cursor: pointer;
  transition: border-color 0.15s ease, color 0.15s ease;
}

.btn-remove:hover {
  border-color: var(--bad);
  color: var(--bad);
}

/* ---------- Results ---------- */

.result-box {
  background: var(--display-bg);
  border-radius: 14px;
  padding: 18px;
  margin-top: 4px;
}

.result-hero {
  text-align: center;
  padding: 10px 0 4px;
}

.result-hero .value {
  color: var(--text-main);
  font-size: 2.2rem;
  font-weight: 700;
  line-height: 1.2;
}

.result-hero .label {
  color: var(--text-muted);
  font-size: 0.85rem;
  margin-top: 4px;
}

.result-grid {
  display: flex;
  flex-direction: column;
  gap: 10px;
}

.result-row {
  display: flex;
  justify-content: space-between;
  align-items: baseline;
  gap: 12px;
  font-size: 0.95rem;
}

.result-row .r-label {
  color: var(--text-muted);
}

.result-row .r-value {
  color: var(--text-main);
  font-weight: 700;
  font-variant-numeric: tabular-nums;
}

.result-row.highlight .r-value {
  color: var(--accent);
  font-size: 1.15rem;
}

.result-row.good .r-value {
  color: var(--good);
}

.result-row.bad .r-value {
  color: var(--bad);
}

hr.divider {
  border: none;
  border-top: 1px solid var(--border);
  margin: 12px 0;
}

/* ---------- Dynamic rows (growth series, split bill, grades) ---------- */

.dyn-list {
  display: flex;
  flex-direction: column;
  gap: 10px;
  margin-bottom: 14px;
}

.dyn-row {
  display: flex;
  align-items: center;
  gap: 8px;
}

.dyn-row input {
  background: var(--input-bg);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 10px 12px;
  color: var(--text-main);
  font-size: 0.95rem;
  font-family: inherit;
  min-width: 0;
}

.dyn-row input:focus {
  outline: none;
  border-color: var(--accent);
}

.dyn-row .grow {
  flex: 1 1 auto;
}

.dyn-row .fixed-sm {
  flex: 0 0 90px;
}

.dyn-row .row-index {
  color: var(--text-muted);
  font-size: 0.8rem;
  flex: 0 0 22px;
  text-align: center;
}

.dyn-table-head {
  display: flex;
  gap: 8px;
  padding: 0 0 4px;
  color: var(--text-muted);
  font-size: 0.75rem;
  text-transform: uppercase;
  letter-spacing: 0.03em;
}

/* ---------- Simple output table (growth results) ---------- */

.out-table {
  width: 100%;
  border-collapse: collapse;
  font-size: 0.85rem;
}

.out-table th,
.out-table td {
  text-align: right;
  padding: 8px 6px;
  border-bottom: 1px solid var(--border);
  color: var(--text-main);
}

.out-table th:first-child,
.out-table td:first-child {
  text-align: left;
  color: var(--text-muted);
}

.out-table thead th {
  color: var(--text-muted);
  text-transform: uppercase;
  font-size: 0.7rem;
  letter-spacing: 0.03em;
}

.out-table .pos {
  color: var(--good);
}

.out-table .neg {
  color: var(--bad);
}

.table-scroll {
  overflow-x: auto;
}

/* ---------- Home hub ---------- */

.hub {
  max-width: 900px;
}

.hub-hero {
  text-align: center;
  margin-bottom: 32px;
}

.hub-hero h1 {
  color: var(--text-main);
  font-size: 2rem;
  margin: 0 0 8px;
}

.hub-hero p {
  color: var(--text-muted);
  margin: 0;
}

.hub-search {
  position: relative;
  max-width: 440px;
  margin: 0 auto 32px;
}

.hub-search-icon {
  position: absolute;
  left: 18px;
  top: 50%;
  transform: translateY(-50%);
  font-size: 0.95rem;
  opacity: 0.6;
  pointer-events: none;
}

.hub-search input {
  width: 100%;
  background: var(--calc-bg);
  border: 1px solid var(--border);
  border-radius: 999px;
  padding: 13px 18px 13px 44px;
  color: var(--text-main);
  font-size: 0.95rem;
  font-family: inherit;
  text-align: left;
  box-shadow: 0 8px 20px var(--shadow);
  transition: border-color 0.15s ease, box-shadow 0.15s ease;
  -webkit-appearance: none;
  appearance: none;
}

.hub-search input::placeholder {
  color: var(--text-muted);
}

.hub-search input:focus {
  outline: none;
  border-color: var(--accent);
  box-shadow: 0 0 0 3px rgba(255, 159, 67, 0.18);
}

.hub-search input::-webkit-search-decoration,
.hub-search input::-webkit-search-cancel-button,
.hub-search input::-webkit-search-results-button,
.hub-search input::-webkit-search-results-decoration {
  -webkit-appearance: none;
}

.hub-no-results {
  text-align: center;
  color: var(--text-muted);
  padding: 24px 0;
}

.hub-group-title {
  color: var(--text-muted);
  font-size: 0.8rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  margin: 28px 0 12px;
}

.hub-group-title:first-of-type {
  margin-top: 0;
}

.hub-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(220px, 1fr));
  gap: 14px;
}

.hub-card {
  display: block;
  background: var(--calc-bg);
  border-radius: 16px;
  padding: 18px;
  text-decoration: none;
  box-shadow: 0 12px 30px var(--shadow);
  transition: transform 0.15s ease, background 0.15s ease;
}

.hub-card:hover {
  transform: translateY(-3px);
  background: #2d3149;
}

.hub-card .icon {
  font-size: 1.6rem;
  margin-bottom: 10px;
  display: block;
}

.hub-card .title {
  color: var(--text-main);
  font-weight: 700;
  font-size: 1rem;
  margin-bottom: 4px;
}

.hub-card .desc {
  color: var(--text-muted);
  font-size: 0.82rem;
  line-height: 1.4;
}

.hub-card[hidden],
.hub-grid[hidden],
.hub-group-title[hidden] {
  display: none;
}

/* ---------- Footer ---------- */

.site-footer {
  margin-top: 32px;
  text-align: center;
  color: var(--text-muted);
  font-size: 0.8rem;
  line-height: 1.7;
}

.site-footer a {
  color: var(--text-muted);
  text-decoration: underline;
  text-decoration-color: var(--border);
  text-underline-offset: 2px;
  transition: color 0.15s ease;
}

.site-footer a:hover {
  color: var(--accent);
}

@media (max-width: 380px) {
  .display-current {
    font-size: 2rem;
  }

  .key {
    padding: 14px 0;
    font-size: 1.05rem;
  }
}

.calculator {
  width: 100%;
  max-width: 360px;
  background: var(--calc-bg);
  border-radius: 24px;
  padding: 20px;
  box-shadow: 0 20px 50px var(--shadow);
}

.display {
  background: var(--display-bg);
  border-radius: 16px;
  padding: 24px 18px 16px;
  margin-bottom: 18px;
  text-align: right;
  overflow: hidden;
}

.display-history {
  min-height: 20px;
  color: var(--text-muted);
  font-size: 0.95rem;
  overflow-x: auto;
  white-space: nowrap;
}

.display-current {
  color: var(--text-main);
  font-size: 2.6rem;
  font-weight: 600;
  overflow-x: auto;
  white-space: nowrap;
  line-height: 1.2;
}

.keys {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 12px;
}

.key {
  border: none;
  border-radius: 14px;
  padding: 18px 0;
  font-size: 1.2rem;
  font-weight: 600;
  color: var(--text-main);
  background: var(--key-num-bg);
  cursor: pointer;
  transition: background 0.15s ease, transform 0.08s ease;
}

.key:hover {
  background: var(--key-num-bg-hover);
}

.key:active {
  transform: scale(0.95);
}

.key-fn {
  background: var(--key-fn-bg);
}

.key-fn:hover {
  background: var(--key-fn-bg-hover);
}

.key-op {
  background: var(--key-op-bg);
  color: #2a1600;
}

.key-op:hover {
  background: var(--key-op-bg-hover);
}

.calculator-sci {
  max-width: 400px;
}

.keys-sci .key {
  font-size: 1rem;
  padding: 16px 0;
}

.key-mode.active {
  background: var(--accent);
  color: #2a1600;
}

.key-eq {
  background: var(--key-eq-bg);
}

.key-eq:hover {
  background: var(--key-eq-bg-hover);
}

.key-zero {
  grid-column: span 2;
}

@media (max-width: 380px) {
  .display-current {
    font-size: 2rem;
  }

  .key {
    padding: 14px 0;
    font-size: 1.05rem;
  }
}