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

:root {
  --text:        #1a1a1a;
  --muted:       #555;
  --accent:      #1a5276;
  --border:      #e0e0e0;
  --bg:          #ffffff;
  --section-gap: 3.5rem;
}

html {
  scroll-behavior: smooth;
}

body {
  font-family: Georgia, "Times New Roman", serif;
  font-size: 1rem;
  line-height: 1.75;
  color: var(--text);
  background: var(--bg);
}

/* ── Layout ── */
.container {
  max-width: 740px;
  margin: 0 auto;
  padding: 0 1.5rem;
}

/* ── Header ── */
header {
  border-bottom: 1px solid var(--border);
  padding: 1.5rem 0;
  position: sticky;
  top: 0;
  background: var(--bg);
  z-index: 10;
}

header .container {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 0.75rem;
}

header h1 {
  font-size: 1.25rem;
  font-weight: normal;
  letter-spacing: 0.01em;
}

nav {
  display: flex;
  gap: 1.5rem;
}

nav a {
  font-family: system-ui, -apple-system, sans-serif;
  font-size: 0.9rem;
  color: var(--muted);
  text-decoration: none;
  letter-spacing: 0.02em;
}

nav a:hover {
  color: var(--accent);
}

/* ── Main ── */
main {
  padding-top: var(--section-gap);
  padding-bottom: var(--section-gap);
}

section {
  margin-bottom: var(--section-gap);
}

section:last-child {
  margin-bottom: 0;
}

h2 {
  font-size: 0.8rem;
  font-family: system-ui, -apple-system, sans-serif;
  font-weight: 600;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--muted);
  margin-bottom: 1.25rem;
  padding-bottom: 0.5rem;
  border-bottom: 1px solid var(--border);
}

p {
  max-width: 60ch;
}

a {
  color: var(--accent);
  text-decoration: none;
}

a:hover {
  text-decoration: underline;
}

/* ── Research / Paper List ── */
.paper-list {
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: 1.5rem;
}

.paper-list li {
  display: flex;
  flex-direction: column;
  gap: 0.2rem;
}

.paper-title {
  font-weight: bold;
  font-size: 1rem;
}

.paper-authors {
  font-size: 0.9rem;
  color: var(--text);
}

.paper-venue {
  font-size: 0.9rem;
  color: var(--muted);
}

.paper-links {
  display: flex;
  gap: 0.75rem;
  margin-top: 0.2rem;
  font-family: system-ui, -apple-system, sans-serif;
  font-size: 0.8rem;
}

.paper-links a {
  border: 1px solid var(--border);
  padding: 0.1rem 0.5rem;
  border-radius: 3px;
  color: var(--muted);
  transition: border-color 0.15s, color 0.15s;
}

.paper-links a:hover {
  border-color: var(--accent);
  color: var(--accent);
  text-decoration: none;
}

/* ── Contact ── */
.contact-list {
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: 0.6rem;
}

.contact-list li {
  display: flex;
  gap: 1rem;
  font-family: system-ui, -apple-system, sans-serif;
  font-size: 0.95rem;
}

.contact-label {
  width: 4.5rem;
  flex-shrink: 0;
  color: var(--muted);
  font-size: 0.85rem;
  padding-top: 0.05rem;
}

/* ── Footer ── */
footer {
  border-top: 1px solid var(--border);
  padding: 1.25rem 0;
  font-family: system-ui, -apple-system, sans-serif;
  font-size: 0.8rem;
  color: var(--muted);
}

/* ── Header: home link + active nav ── */
.home-link {
  color: inherit;
  text-decoration: none;
}

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

/* ── Calculator ── */
.calc-form {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 2rem;
  margin-bottom: 2rem;
}

.calc-group-label {
  font-family: system-ui, -apple-system, sans-serif;
  font-size: 0.75rem;
  font-weight: 600;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--muted);
  margin-bottom: 1rem;
}

.calc-group {
  display: flex;
  flex-direction: column;
  gap: 1.25rem;
}

.calc-field {
  display: flex;
  flex-direction: column;
  gap: 0.4rem;
}

.calc-field label {
  font-family: system-ui, -apple-system, sans-serif;
  font-size: 0.9rem;
  color: var(--text);
}

.calc-input-row {
  display: flex;
  align-items: center;
  border: 1px solid var(--border);
  border-radius: 4px;
  overflow: hidden;
  transition: border-color 0.15s;
}

.calc-input-row:focus-within {
  border-color: var(--accent);
}

.calc-input-row input {
  flex: 1;
  border: none;
  outline: none;
  padding: 0.6rem 0.75rem;
  font-family: system-ui, -apple-system, sans-serif;
  font-size: 1.1rem;
  color: var(--text);
  background: transparent;
  min-width: 0;
  -moz-appearance: textfield;
}

.calc-input-row input::-webkit-outer-spin-button,
.calc-input-row input::-webkit-inner-spin-button {
  -webkit-appearance: none;
}

.calc-unit {
  padding: 0 0.75rem;
  font-family: system-ui, -apple-system, sans-serif;
  font-size: 0.85rem;
  color: var(--muted);
  border-left: 1px solid var(--border);
  line-height: 2.6rem;
  background: #f8f8f8;
  flex-shrink: 0;
}

.calc-hint {
  font-family: system-ui, -apple-system, sans-serif;
  font-size: 0.8rem;
  color: var(--muted);
  max-width: none;
}

.calc-results {
  border: 1px solid var(--border);
  border-radius: 4px;
  overflow: hidden;
  transition: border-color 0.15s;
}

.calc-results--ready {
  border-color: var(--accent);
}

.calc-result-row {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0.85rem 1.25rem;
  background: #f8f8f8;
  border-bottom: 1px solid var(--border);
}

.calc-result-row--total {
  background: #fff;
  border-bottom: none;
}

.calc-results--ready .calc-result-row--total {
  background: #eef3f8;
}

.calc-result-label {
  font-family: system-ui, -apple-system, sans-serif;
  font-size: 0.9rem;
  color: var(--muted);
}

.calc-result-value {
  font-family: system-ui, -apple-system, sans-serif;
  font-size: 1.4rem;
  font-weight: 600;
  color: var(--text);
  display: flex;
  align-items: baseline;
  gap: 0.35rem;
}

.calc-result-row--total .calc-result-value {
  font-size: 1.6rem;
}

.calc-result-unit {
  font-size: 0.9rem;
  font-weight: normal;
  color: var(--muted);
}

.calc-error {
  font-family: system-ui, -apple-system, sans-serif;
  font-size: 0.85rem;
  color: #c0392b;
  padding: 0.75rem 1.25rem;
  background: #fdf0ee;
  border-top: 1px solid #f5c6c0;
}

/* ── Log measurement ── */
.calc-log {
  margin-top: 1.25rem;
  padding-top: 1.25rem;
  border-top: 1px solid var(--border);
  display: flex;
  flex-direction: column;
  gap: 0.85rem;
}

.calc-log-notes {
  max-width: 26rem;
}

.calc-log-notes input[type="text"] {
  width: 100%;
  border: none;
  outline: none;
  padding: 0.6rem 0.75rem;
  font-family: system-ui, -apple-system, sans-serif;
  font-size: 0.95rem;
  color: var(--text);
  background: transparent;
  min-width: 0;
}

.calc-log-action {
  display: flex;
  align-items: center;
  gap: 1rem;
  flex-wrap: wrap;
}

.log-btn {
  font-family: system-ui, -apple-system, sans-serif;
  font-size: 0.875rem;
  color: var(--accent);
  background: none;
  border: 1px solid var(--accent);
  border-radius: 4px;
  padding: 0.45rem 1rem;
  cursor: pointer;
  transition: background 0.15s, color 0.15s;
}

.log-btn:hover:not(:disabled) {
  background: var(--accent);
  color: #fff;
}

.log-btn:disabled {
  opacity: 0.6;
  cursor: default;
}

.log-status {
  font-family: system-ui, -apple-system, sans-serif;
  font-size: 0.85rem;
  color: var(--muted);
}

.log-status--err {
  color: #c0392b;
}

/* ── Calibration (collapsible) ── */
.cal-details {
  margin-bottom: var(--section-gap);
}

.cal-details > .cal-summary {
  font-size: 0.8rem;
  font-family: system-ui, -apple-system, sans-serif;
  font-weight: 600;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--muted);
  padding: 0.75rem 0;
  border-top: 1px solid var(--border);
  border-bottom: 1px solid var(--border);
  cursor: pointer;
  list-style: none;
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 0;
}

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

.cal-details > .cal-summary::after {
  content: '›';
  font-size: 1.1rem;
  font-weight: 300;
  color: var(--muted);
  transition: transform 0.2s;
  line-height: 1;
}

.cal-details[open] > .cal-summary::after {
  transform: rotate(90deg);
}

.cal-details[open] > .cal-summary {
  border-bottom: none;
  margin-bottom: 1.25rem;
}

/* ── Calibration blocks ── */
.cal-block {
  border: 1px solid var(--border);
  border-radius: 4px;
  padding: 1.25rem;
  margin-bottom: 1rem;
}

.cal-block:last-child {
  margin-bottom: 0;
}

.cal-block-title {
  font-family: system-ui, -apple-system, sans-serif;
  font-size: 0.875rem;
  font-weight: 600;
  color: var(--text);
  margin-bottom: 0.4rem;
}

.cal-desc {
  font-family: system-ui, -apple-system, sans-serif;
  font-size: 0.825rem;
  color: var(--muted);
  max-width: 62ch;
  margin-bottom: 1.25rem;
  line-height: 1.6;
}

.cal-form-3 {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 1rem;
  margin-bottom: 1rem;
}

.cal-form-3 > * {
  min-width: 0;
}

.cal-output {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0.65rem 1rem;
  border: 1px solid var(--border);
  border-radius: 4px;
  background: #f8f8f8;
  transition: border-color 0.15s, background 0.15s;
}

.cal-output--ready {
  border-color: var(--accent);
  background: #eef3f8;
}

.cal-output--secondary {
  margin-top: 0.5rem;
}

.cal-output--secondary .cal-output-value {
  font-size: 1rem;
  color: var(--muted);
}

.cal-output-label {
  font-family: system-ui, -apple-system, sans-serif;
  font-size: 0.85rem;
  color: var(--muted);
}

.cal-output-value {
  font-family: system-ui, -apple-system, sans-serif;
  font-size: 1.2rem;
  font-weight: 600;
  color: var(--text);
}

.cal-toggle-label {
  display: flex;
  align-items: center;
  gap: 0.6rem;
  font-family: system-ui, -apple-system, sans-serif;
  font-size: 0.9rem;
  color: var(--text);
  cursor: pointer;
}

.cal-toggle-label input[type="checkbox"] {
  width: 1rem;
  height: 1rem;
  accent-color: var(--accent);
  cursor: pointer;
  flex-shrink: 0;
}

#pump-cal-section {
  margin-top: 1.25rem;
}

.label-muted {
  font-weight: normal;
  font-size: 0.85rem;
  color: var(--muted);
}

/* ── Responsive ── */
@media (max-width: 520px) {
  header .container {
    flex-direction: column;
  }
  nav {
    gap: 1rem;
  }
  .calc-form {
    grid-template-columns: 1fr;
  }
  .cal-form-3 {
    grid-template-columns: 1fr;
  }
}