:root {
  --brand: #1e40af;
  --border: #dcdcdc;
  --grey: #555;
  --gap: 1.4rem;
}
* { box-sizing: border-box; margin: 0; padding: 0; }
body {
  font-family: system-ui, sans-serif;
  line-height: 1.6;
  color: #222;
}
main {
  max-width: 760px;
  margin: auto;
  padding: 2rem 1rem;
}
h1 {
  margin-bottom: .6rem;
}
.intro {
  margin-bottom: 1.2rem;
  color: var(--grey);
}

.mhc-calculator {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: var(--gap);
  margin-bottom: 2rem;
}
.mhc-calculator label {
  display: contents;
}
.mhc-calculator span {
  display: block;
  margin-bottom: .3rem;
  color: var(--grey);
}
.mhc-calculator input,
.mhc-calculator select {
  width: 100%;
  padding: .5rem;
  border: 1px solid var(--border);
  border-radius: 4px;
  font: inherit;
}
.mhc-calculator button {
  grid-column: 1 / -1;
  padding: .6rem;
  border: none;
  border-radius: 4px;
  background: var(--brand);
  color: #fff;
  font-weight: 600;
  cursor: pointer;
}
.mhc-calculator button:hover {
  background: #16357b;
}

.hidden {
  display: none;
}

.mhc-error {
  grid-column: 1 / -1;
  color: #d00;
  font-size: .9rem;
}
.mhc-result {
  grid-column: 1 / -1;
  margin-top: 1rem;
  font-weight: 700;
}