/* Minimal, responsive calculator. Grid does all the layout work. */
:root {
  --bg: #f0f0f3;
  --calc-bg: #ffffff;
  --key: #e9e9ee;
  --key-op: #ff9500;
  --key-fn: #d4d4dc;
  --text: #1c1c1e;
  --text-op: #ffffff;
}

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

body {
  min-height: 100vh;
  display: grid;
  place-items: center;
  padding: 1rem;
  background: var(--bg);
  font-family: system-ui, -apple-system, sans-serif;
}

.calc {
  width: min(100%, 340px);
  padding: 1rem;
  background: var(--calc-bg);
  border-radius: 1.25rem;
  box-shadow: 0 10px 30px rgba(0, 0, 0, 0.12);
}

.calc__screen {
  padding: 0.75rem 0.5rem 1rem;
  margin-bottom: 1rem;
  text-align: right;
}

/* stacked past calculations, scrolls once it fills up */
.calc__history {
  max-height: 6rem;
  overflow-y: auto;
  font-size: clamp(0.9rem, 4vw, 1.15rem);
  color: #8a8a8e;
  word-break: break-all;
}
.calc__history div { padding: 0.1rem 0; }

/* big focused line: the expression being typed / current result */
.calc__display {
  display: block;
  min-height: 3rem;
  font-size: clamp(2rem, 12vw, 3rem);
  font-weight: 300;
  color: var(--text);
  word-break: break-all;
  overflow: hidden;
}

/* small muted line: live value of the expression above */
.calc__preview {
  min-height: 1.4rem;
  font-size: clamp(1rem, 5vw, 1.35rem);
  color: #8a8a8e;
  word-break: break-all;
}

.calc__keys {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 0.6rem;
}

.key {
  padding: 1rem 0;
  font-size: 1.35rem;
  border: none;
  border-radius: 0.75rem;
  background: var(--key);
  color: var(--text);
  cursor: pointer;
  transition: filter 0.1s ease;
}

.key:hover { filter: brightness(0.95); }
.key:active { filter: brightness(0.88); }
.key:focus-visible { outline: 3px solid var(--key-op); outline-offset: 2px; }

.key--op, .key--eq { background: var(--key-op); color: var(--text-op); }
.key--fn { background: var(--key-fn); }
.key--zero { grid-column: span 2; }

/* highlight the operator that's currently pending */
.key--op[aria-pressed="true"] { filter: brightness(0.85); }