/* Minimal, fast, readable */
* { box-sizing: border-box; }
:root { --gap: 12px; }

body {
  margin: 0;
  padding: var(--gap);
  font-family: system-ui, -apple-system, Segoe UI, Roboto, sans-serif;
  line-height: 1.6;
  color: #222;
  background: #fff;
}

.wrap { max-width: 960px; margin: 0 auto; }

.header h1 { margin: 0 0 4px; font-size: 28px; }
.muted { color: #666; font-size: 14px; margin: 0 0 16px; }

.cols {
  display: grid;
  gap: var(--gap);
  grid-template-columns: 1fr;
}
@media (min-width: 900px) {
  .cols { grid-template-columns: 1fr 1fr; }
}
.grid { display: grid; gap: var(--gap); }

.card {
  border: 1px solid #ddd;
  border-radius: 6px;
  padding: 12px;
  background: #fff;
}

h3 { margin: 0 0 10px; font-size: 18px; }
h4 { margin: 12px 0 6px; font-size: 13px; color: #555; text-transform: uppercase; letter-spacing: .02em; }

textarea, input[type="number"] {
  width: 100%;
  padding: 8px 10px;
  border: 1px solid #bbb;
  border-radius: 6px;
  font-family: ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
  font-size: 14px;
  min-height: 120px;
  resize: vertical;
}
input[type="number"] { min-height: auto; font-family: inherit; }

.row {
  display: flex;
  gap: var(--gap);
  flex-wrap: wrap;
  align-items: center;
  margin-top: 8px;
}

.btn {
  padding: 8px 10px;
  border: 1px solid #bbb;
  border-radius: 6px;
  background: #fafafa;
  color: #111;
  font-size: 14px;
  cursor: pointer;
}
.btn:hover { background: #f0f0f0; }
.btn:active { background: #e9e9e9; }


.btn-operation:hover { background: #096aa6; border-color: #096aa6; }

.btn-clear {
  background: #c62828;
  border-color: #c62828;
  color: #fff;
}
.btn-clear:hover { background: #b71c1c; border-color: #b71c1c; }

.btn-example .btn-operation { font-size: 12px; padding: 6px 8px; }

.result-display {
  background: #f8f9fa;
  border: 1px solid #e6e6e6;
  border-radius: 6px;
  padding: 12px;
  min-height: 100px;
  font-family: ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
  font-size: 14px;
  white-space: pre-wrap;
  overflow-x: auto;
}

.error-display {
  margin-top: 8px;
  padding: 10px;
  border-radius: 6px;
  border: 1px solid #f6c6c6;
  background: #ffecec;
  color: #a40000;
  font-size: 14px;
}

/* Mobile: full-width buttons if you want even simpler tapping */
@media (max-width: 600px) {
  .row .btn { flex: 1; }
}