* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: Arial, sans-serif;
  background-color: #111;
  color: #f4f4f4;
  display: flex;
  align-items: center;
  justify-content: center;
  min-height: 100vh;
}

.calculator {
  background: #1e1e1e;
  border-radius: 8px;
  padding: 1.5rem;
  width: min(480px, 90vw);
  box-shadow: 0 8px 24px rgba(0, 0, 0, 0.4);
  display: grid;
  grid-template-rows: auto auto auto 1fr auto;
  gap: 1rem;
}

header h1 {
  margin: 0 0 0.5rem 0;
  font-size: 1.75rem;
}

header p {
  margin: 0;
  font-size: 0.9rem;
  color: #c7c7c7;
}

.display {
  background: #000;
  border-radius: 6px;
  padding: 1rem;
}

.display__title {
  margin: 0 0 0.5rem 0;
  font-size: 1rem;
  color: #9adbff;
}

.stack {
  list-style: none;
  margin: 0;
  padding: 0;
  min-height: 8rem;
  display: flex;
  flex-direction: column;
  justify-content: flex-end;
  gap: 0.25rem;
}

.stack li {
  display: flex;
  justify-content: space-between;
  align-items: center;
  background: #1f2a37;
  border-radius: 4px;
  padding: 0.4rem 0.6rem;
  font-family: 'Courier New', Courier, monospace;
}

.stack li.empty {
  opacity: 0.4;
}

.stack__label {
  color: #74d2ff;
  margin-right: 0.5rem;
}

.input {
  display: flex;
  gap: 0.5rem;
}

.input input {
  flex: 1;
  font-size: 1.1rem;
  padding: 0.5rem 0.75rem;
  border-radius: 4px;
  border: 1px solid #444;
  background: #111;
  color: inherit;
}

.input button {
  padding: 0 0.75rem;
  font-size: 1rem;
}

.controls {
  display: grid;
  grid-template-columns: 2fr 1fr;
  gap: 1rem;
}

.pad {
  display: grid;
  gap: 0.5rem;
}

.pad--numbers {
  grid-template-columns: repeat(3, 1fr);
}

.pad--ops {
  grid-template-columns: repeat(4, 1fr);
}

button {
  background: #29313d;
  color: inherit;
  border: none;
  border-radius: 4px;
  padding: 0.6rem;
  font-size: 1rem;
  cursor: pointer;
  transition: background 0.15s;
}

button:hover,
button:focus {
  background: #3a4656;
  outline: none;
}

button:active {
  background: #74d2ff;
  color: #000;
}

.log {
  min-height: 1.4rem;
  font-size: 0.95rem;
  color: #9adbff;
}

.log p {
  margin: 0;
}

.status--error {
  color: #ff8383;
}

.status--success {
  color: #a9ff9f;
}

.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}