html, body {
  width: 100%;
  min-height: 100vh;
}

body {
  overflow-x: hidden;
}

/* ========== 背景canvas ========== */

#bg-canvas {
  position: fixed;
  inset: 0;
  width: 100vw;
  height: 100vh;
  z-index: 0;
  pointer-events: none;
}

/* ========== レイアウト ========== */

main {
  position: relative;
  z-index: 2;
  max-width: 48rem;
  margin: 0 auto;
  padding: 2rem 1.25rem;
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
}

.calc-wrap {
  width: 100%;
  max-width: 22rem;
  text-align: center;
}

.calc-title {
  font-size: 1.5rem;
  font-weight: 700;
  letter-spacing: 0.05em;
  margin-bottom: 0.25rem;
}

.calc-subtitle {
  color: var(--wa-ink-light);
  font-size: 0.85rem;
  line-height: 1.7;
  margin-bottom: 1.5rem;
}

/* ========== 電卓本体 ========== */

.calc {
  background-color: var(--wa-white);
  border: 1px solid var(--wa-ink);
  border-radius: 6px;
  padding: 1.25rem;
  box-shadow: 6px 6px 0 var(--wa-ink);
}

.calc-display {
  background-color: var(--wa-sea-light);
  border: 1px solid var(--wa-ink);
  border-radius: 4px;
  padding: 0.75rem 0.875rem;
  margin-bottom: 0.875rem;
  text-align: right;
  min-height: 4rem;
  display: flex;
  flex-direction: column;
  justify-content: flex-end;
  font-family: "Avenir", "Helvetica Neue", Arial, sans-serif;
}

.calc-expr {
  font-size: 0.8rem;
  color: var(--wa-gray);
  min-height: 1rem;
  word-break: break-all;
  line-height: 1.4;
}

.calc-result {
  font-size: 1.75rem;
  font-weight: 700;
  margin-top: 0.25rem;
  word-break: break-all;
  line-height: 1.2;
}

/* ========== キー ========== */

.calc-keys {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 0.4rem;
}

.key {
  font-family: inherit;
  font-size: 1rem;
  font-weight: 700;
  padding: 0.875rem 0;
  background-color: var(--wa-white);
  color: var(--wa-ink);
  border: 1px solid var(--wa-ink);
  border-radius: 4px;
  cursor: pointer;
  transition: background-color 0.12s;
  user-select: none;
  -webkit-tap-highlight-color: transparent;
}

.key:hover {
  background-color: var(--wa-orange-pale);
}

.key:active {
  background-color: var(--wa-orange-light);
}

.key--op {
  color: var(--wa-orange-dark);
}

.key--util {
  color: var(--wa-gray);
}

.key--eq {
  background-color: var(--wa-orange);
  color: var(--wa-white);
  border-color: var(--wa-orange);
  grid-column: span 2;
}

.key--eq:hover {
  background-color: var(--wa-orange-dark);
  border-color: var(--wa-orange-dark);
}

.key--eq:active {
  background-color: var(--wa-orange-dark);
}

/* ========== リセット・カウンター ========== */

.calc-reset {
  display: block;
  width: 100%;
  margin-top: 0.6rem;
  padding: 0.55rem 0;
  background: transparent;
  color: var(--wa-ink-light);
  border: 1px solid var(--wa-ink);
  border-radius: 4px;
  font-family: inherit;
  font-size: 0.8rem;
  letter-spacing: 0.05em;
  cursor: pointer;
  transition: background-color 0.12s, color 0.12s;
}

.calc-reset:hover {
  background-color: var(--wa-ink);
  color: var(--wa-white);
}

.calc-counter {
  margin-top: 0.6rem;
  text-align: center;
  font-size: 0.75rem;
  color: var(--wa-gray);
  letter-spacing: 0.05em;
}

/* ========== Responsive ========== */

@media (max-width: 480px) {
  .calc-title {
    font-size: 1.35rem;
  }
  .calc-result {
    font-size: 1.5rem;
  }
  .key {
    font-size: 0.95rem;
    padding: 0.75rem 0;
  }
}