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

body {
  font-family: 'Segoe UI', Arial, sans-serif;
  background: #0a0f1e;
  color: #e0e6f0;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  align-items: center;
  padding: 40px 20px;
}

/* ── HEADER ── */
header {
  text-align: center;
  margin-bottom: 36px;
}

header h1 {
  font-size: 1.9rem;
  color: #7eb8f7;
  letter-spacing: 1px;
  margin-bottom: 6px;
}

header p {
  color: #8899bb;
  font-size: 0.95rem;
}

/* ── FORMULA BOX ── */
.formula-box {
  background: #111827;
  border: 1px solid #1e3a5f;
  border-radius: 10px;
  padding: 18px 28px;
  margin-bottom: 32px;
  text-align: center;
  max-width: 520px;
  width: 100%;
}

.formula-box .formula {
  font-size: 1.3rem;
  color: #7eb8f7;
  font-style: italic;
  letter-spacing: 1px;
  margin-bottom: 8px;
}

.formula-box .legend {
  font-size: 0.82rem;
  color: #6677aa;
  line-height: 1.7;
}

/* ── CARD ── */
.card {
  background: #111827;
  border: 1px solid #1e3a5f;
  border-radius: 12px;
  padding: 28px 32px;
  max-width: 520px;
  width: 100%;
  margin-bottom: 28px;
}

.card h2 {
  font-size: 1rem;
  color: #7eb8f7;
  margin-bottom: 20px;
  text-transform: uppercase;
  letter-spacing: 1px;
}

.ref-card {
  max-width: 520px;
}

/* ── FORM ── */
.field {
  margin-bottom: 18px;
}

label {
  display: block;
  font-size: 0.85rem;
  color: #8899bb;
  margin-bottom: 6px;
}

input,
select {
  width: 100%;
  background: #0d1520;
  border: 1px solid #1e3a5f;
  border-radius: 6px;
  color: #e0e6f0;
  font-size: 1rem;
  padding: 10px 14px;
  outline: none;
  transition: border-color 0.2s;
}

input:focus,
select:focus {
  border-color: #7eb8f7;
}

button {
  width: 100%;
  background: linear-gradient(135deg, #1a4a8a, #2563c4);
  color: #fff;
  border: none;
  border-radius: 8px;
  font-size: 1rem;
  font-weight: 600;
  padding: 13px;
  cursor: pointer;
  letter-spacing: 0.5px;
  transition: opacity 0.2s;
  margin-top: 6px;
}

button:hover {
  opacity: 0.88;
}

/* ── RESULTS ── */
.results {
  display: none;
  max-width: 520px;
  width: 100%;
}

.result-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 14px;
  margin-bottom: 20px;
}

.result-item {
  background: #0d1520;
  border: 1px solid #1e3a5f;
  border-radius: 8px;
  padding: 16px;
  text-align: center;
}

.result-item .val {
  font-size: 1.5rem;
  font-weight: 700;
  color: #7eb8f7;
}

.result-item .unit {
  font-size: 0.75rem;
  color: #4466aa;
  margin-top: 2px;
}

.result-item .lbl {
  font-size: 0.78rem;
  color: #8899bb;
  margin-top: 6px;
}

/* ── MASS BAR ── */
.mass-bar-wrap {
  background: #0d1520;
  border: 1px solid #1e3a5f;
  border-radius: 8px;
  padding: 16px 18px;
  margin-bottom: 14px;
}

.mass-bar-wrap .bar-label {
  display: flex;
  justify-content: space-between;
  font-size: 0.8rem;
  color: #8899bb;
  margin-bottom: 8px;
}

.bar-track {
  height: 14px;
  background: #1a2535;
  border-radius: 7px;
  overflow: hidden;
}

.bar-fill-fuel {
  height: 100%;
  background: linear-gradient(90deg, #2563c4, #7eb8f7);
  border-radius: 7px;
  transition: width 0.5s;
}

/* ── INSIGHT ── */
.insight {
  background: #0d1520;
  border-left: 3px solid #7eb8f7;
  border-radius: 0 8px 8px 0;
  padding: 14px 16px;
  font-size: 0.85rem;
  color: #8899bb;
  line-height: 1.6;
}

.insight strong {
  color: #c0d8f7;
}

/* ── REFERENCE TABLE ── */
.propellant-table {
  width: 100%;
  border-collapse: collapse;
  font-size: 0.82rem;
  margin-top: 8px;
}

.propellant-table th {
  color: #4466aa;
  text-align: left;
  padding: 4px 8px;
  border-bottom: 1px solid #1e3a5f;
}

.propellant-table td {
  padding: 6px 8px;
  color: #8899bb;
  border-bottom: 1px solid #0d1a2a;
}

.propellant-table tr:hover td {
  color: #c0d8f7;
}

/* ── FOOTER ── */
footer {
  margin-top: 40px;
  font-size: 0.78rem;
  color: #334466;
  text-align: center;
}

footer a {
  color: #4466aa;
  text-decoration: none;
}