.calculator {
  max-width: 320px;
  margin: 0 auto;
  background-color: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  overflow: hidden;
}

.display {
  padding: 24px 20px;
  text-align: right;
  font-size: 36px;
  font-weight: 300;
  font-family: var(--font-mono);
  background-color: var(--bg-surface);
  border-bottom: 1px solid var(--border);
  min-height: 80px;
  display: flex;
  align-items: center;
  justify-content: flex-end;
  word-break: break-all;
}

.buttons {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 1px;
  background-color: var(--border);
}

.btn-calc {
  padding: 18px;
  font-size: 20px;
  font-weight: 500;
  border: none;
  background-color: var(--bg-card);
  color: var(--text-primary);
  cursor: pointer;
  transition: background-color 0.15s;
  font-family: var(--font-family);
}

.btn-calc:hover {
  background-color: var(--bg-hover);
}

.btn-calc:active {
  background-color: var(--border);
}

.btn-operator {
  background-color: var(--bg-surface);
  color: var(--accent);
}

.btn-operator:hover {
  background-color: var(--bg-hover);
}

.btn-clear {
  color: var(--error);
}

.btn-equals {
  background-color: var(--accent);
  color: #ffffff;
}

.btn-equals:hover {
  background-color: var(--accent-hover);
}

.btn-zero {
  grid-column: span 2;
}

/* ================================
   MOBILE RESPONSIVE — Tool Page Fix
   ================================ */

/* Inherit from global */
input, textarea, select {
  font-size: 16px; /* prevents iOS auto-zoom */
  width: 100%;
  max-width: 100%;
}

/* Responsive tool UI */
@media (max-width: 540px) {
  .tool-actions {
    flex-direction: column;
  }

  .btn {
    width: 100%;
    justify-content: center;
  }
}