/* ============================================================
   Engineering Tools — Shared Stylesheet
   Clean & Professional Theme
   ============================================================ */

*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

:root {
  --blue:       #2563eb;
  --blue-light: #eff6ff;
  --blue-dark:  #1d4ed8;
  --text:       #1e293b;
  --text-muted: #64748b;
  --border:     #e2e8f0;
  --bg:         #f8fafc;
  --white:      #ffffff;
  --success:    #16a34a;
  --radius:     6px;
  --shadow:     0 1px 3px rgba(0,0,0,.08), 0 1px 2px rgba(0,0,0,.05);
  --shadow-md:  0 4px 6px -1px rgba(0,0,0,.08), 0 2px 4px -1px rgba(0,0,0,.05);
}

body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  font-size: 15px;
  line-height: 1.6;
  color: var(--text);
  background: var(--bg);
  min-height: 100vh;
}

/* ---- Header ---- */
.site-header {
  background: var(--white);
  border-bottom: 1px solid var(--border);
  padding: 0 1.5rem;
  height: 56px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  position: sticky;
  top: 0;
  z-index: 100;
  box-shadow: var(--shadow);
}

.site-header .logo {
  font-size: 1.05rem;
  font-weight: 700;
  color: var(--text);
  text-decoration: none;
  display: flex;
  align-items: center;
  gap: .45rem;
}

.site-header .logo span {
  color: var(--blue);
}

.site-header nav a {
  font-size: .875rem;
  color: var(--text-muted);
  text-decoration: none;
  margin-left: 1.25rem;
  transition: color .15s;
}

.site-header nav a:hover,
.site-header nav a.active { color: var(--blue); }

/* ---- Layout ---- */
.layout {
  display: flex;
  max-width: 1200px;
  margin: 0 auto;
  padding: 2rem 1.5rem;
  gap: 1.75rem;
  align-items: flex-start;
}

/* ---- Sidebar ---- */
.sidebar {
  width: 220px;
  flex-shrink: 0;
  position: sticky;
  top: 72px;
}

.sidebar-section { margin-bottom: 1.5rem; }

.sidebar-label {
  font-size: .7rem;
  font-weight: 700;
  letter-spacing: .07em;
  text-transform: uppercase;
  color: var(--text-muted);
  padding: 0 .5rem .4rem;
  border-bottom: 1px solid var(--border);
  margin-bottom: .5rem;
}

.sidebar a {
  display: block;
  padding: .4rem .5rem;
  border-radius: var(--radius);
  font-size: .875rem;
  color: var(--text-muted);
  text-decoration: none;
  transition: background .12s, color .12s;
}

.sidebar a:hover { background: var(--blue-light); color: var(--blue); }
.sidebar a.active { background: var(--blue-light); color: var(--blue); font-weight: 600; }

/* ---- Main content ---- */
.main { flex: 1; min-width: 0; }

.page-title {
  font-size: 1.5rem;
  font-weight: 700;
  color: var(--text);
  margin-bottom: .25rem;
}

.page-subtitle {
  font-size: .9rem;
  color: var(--text-muted);
  margin-bottom: 1.75rem;
}

/* ---- Cards ---- */
.card {
  background: var(--white);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.5rem;
  box-shadow: var(--shadow);
  margin-bottom: 1.25rem;
}

.card h2 {
  font-size: 1rem;
  font-weight: 600;
  margin-bottom: 1rem;
  color: var(--text);
}

/* ---- Form elements ---- */
.form-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(180px, 1fr));
  gap: .85rem;
}

.form-group { display: flex; flex-direction: column; gap: .3rem; }

label {
  font-size: .8rem;
  font-weight: 600;
  color: var(--text-muted);
  letter-spacing: .02em;
  text-transform: uppercase;
}

.input-wrap { position: relative; display: flex; }

input[type=number], input[type=text], select {
  width: 100%;
  padding: .5rem .75rem;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  font-size: .95rem;
  color: var(--text);
  background: var(--white);
  transition: border-color .15s, box-shadow .15s;
  outline: none;
  -moz-appearance: textfield;
}

input[type=number]::-webkit-inner-spin-button,
input[type=number]::-webkit-outer-spin-button { -webkit-appearance: none; }

input:focus, select:focus {
  border-color: var(--blue);
  box-shadow: 0 0 0 3px rgba(37,99,235,.12);
}

.input-unit {
  display: flex;
  align-items: center;
  padding: .5rem .65rem;
  background: var(--bg);
  border: 1px solid var(--border);
  border-left: none;
  border-radius: 0 var(--radius) var(--radius) 0;
  font-size: .8rem;
  color: var(--text-muted);
  white-space: nowrap;
}

.input-wrap input { border-radius: var(--radius) 0 0 var(--radius); }

/* ---- Buttons ---- */
.btn {
  display: inline-flex;
  align-items: center;
  gap: .4rem;
  padding: .55rem 1.1rem;
  border-radius: var(--radius);
  font-size: .9rem;
  font-weight: 600;
  cursor: pointer;
  border: none;
  transition: background .15s, box-shadow .15s;
}

.btn-primary { background: var(--blue); color: #fff; }
.btn-primary:hover { background: var(--blue-dark); box-shadow: var(--shadow-md); }
.btn-secondary { background: var(--bg); color: var(--text); border: 1px solid var(--border); }
.btn-secondary:hover { background: var(--border); }

.actions { margin-top: 1.1rem; display: flex; gap: .6rem; align-items: center; }

/* ---- Results ---- */
.results {
  background: var(--blue-light);
  border: 1px solid #bfdbfe;
  border-radius: var(--radius);
  padding: 1rem 1.25rem;
  margin-top: 1.1rem;
  display: none;
}

.results.visible { display: block; }

.results h3 {
  font-size: .8rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: .07em;
  color: var(--blue);
  margin-bottom: .65rem;
}

.result-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(160px, 1fr));
  gap: .6rem;
}

.result-item {
  background: var(--white);
  border: 1px solid #bfdbfe;
  border-radius: var(--radius);
  padding: .6rem .85rem;
}

.result-label {
  font-size: .75rem;
  font-weight: 600;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: .05em;
}

.result-value {
  font-size: 1.15rem;
  font-weight: 700;
  color: var(--text);
  margin-top: .1rem;
}

.result-value .unit {
  font-size: .8rem;
  font-weight: 500;
  color: var(--text-muted);
  margin-left: .2rem;
}

/* ---- Formula display ---- */
.formula-block {
  background: #f1f5f9;
  border-left: 3px solid var(--blue);
  border-radius: 0 var(--radius) var(--radius) 0;
  padding: .65rem 1rem;
  font-family: "SFMono-Regular", Consolas, "Liberation Mono", Menlo, monospace;
  font-size: .875rem;
  color: var(--text);
  margin-bottom: 1rem;
}

/* ---- Tables ---- */
.data-table {
  width: 100%;
  border-collapse: collapse;
  font-size: .875rem;
}

.data-table th {
  background: #f1f5f9;
  font-weight: 700;
  font-size: .75rem;
  text-transform: uppercase;
  letter-spacing: .05em;
  color: var(--text-muted);
  padding: .65rem .85rem;
  text-align: left;
  border-bottom: 2px solid var(--border);
}

.data-table td {
  padding: .55rem .85rem;
  border-bottom: 1px solid var(--border);
  color: var(--text);
}

.data-table tr:last-child td { border-bottom: none; }
.data-table tr:hover td { background: var(--blue-light); }

/* ---- Alert / info box ---- */
.info-box {
  background: #fefce8;
  border: 1px solid #fde68a;
  border-radius: var(--radius);
  padding: .75rem 1rem;
  font-size: .85rem;
  color: #92400e;
  margin-top: .85rem;
}

/* ---- Error ---- */
.error { color: #dc2626; font-size: .825rem; margin-top: .4rem; display: none; }
.error.visible { display: block; }

/* ---- Homepage grid ---- */
.tool-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(260px, 1fr));
  gap: 1rem;
  margin-bottom: 2rem;
}

.tool-card {
  background: var(--white);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.25rem;
  text-decoration: none;
  color: inherit;
  box-shadow: var(--shadow);
  transition: box-shadow .15s, border-color .15s, transform .12s;
  display: flex;
  flex-direction: column;
  gap: .3rem;
}

.tool-card:hover {
  box-shadow: var(--shadow-md);
  border-color: #bfdbfe;
  transform: translateY(-1px);
}

.tool-card-icon {
  font-size: 1.5rem;
  margin-bottom: .25rem;
}

.tool-card-title {
  font-size: .975rem;
  font-weight: 700;
  color: var(--text);
}

.tool-card-desc {
  font-size: .825rem;
  color: var(--text-muted);
  line-height: 1.45;
}

.section-heading {
  font-size: .75rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: .08em;
  color: var(--blue);
  margin-bottom: .75rem;
  margin-top: .25rem;
  display: flex;
  align-items: center;
  gap: .5rem;
}

.section-heading::after {
  content: '';
  flex: 1;
  height: 1px;
  background: var(--border);
}

/* ---- Responsive ---- */
@media (max-width: 768px) {
  .layout { flex-direction: column; padding: 1rem; }
  .sidebar { width: 100%; position: static; }
  .form-grid { grid-template-columns: 1fr 1fr; }
  .site-header nav { display: none; }
}

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

/* ── Smart unit input ── */
.unit-input {
  display: inline-flex;
  width: fit-content;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  overflow: hidden;
  transition: border-color .15s, box-shadow .15s;
}
.unit-input:focus-within {
  border-color: var(--blue);
  box-shadow: 0 0 0 3px rgba(37,99,235,.12);
}
.unit-input > input[type=number] {
  flex: 0 0 auto;
  width: 105px !important;
  border: none !important;
  border-radius: 0 !important;
  box-shadow: none !important;
  outline: none;
  padding: .5rem .75rem;
  font-size: .95rem;
  color: var(--text);
  background: var(--white);
  -moz-appearance: textfield;
}
.unit-input > input[type=number]::-webkit-inner-spin-button,
.unit-input > input[type=number]::-webkit-outer-spin-button { -webkit-appearance: none; }
.unit-input > select {
  flex: 0 0 auto;
  width: auto !important;
  border: none !important;
  border-left: 1px solid var(--border) !important;
  border-radius: 0 !important;
  box-shadow: none !important;
  padding: .5rem .55rem .5rem .65rem;
  font-size: .85rem;
  font-weight: 600;
  color: var(--text-muted);
  background: var(--bg);
  cursor: pointer;
  outline: none;
}