src/style.css

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  min-height: 100vh;
  font-family: Inter, ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  background: #f6f7f9;
  color: #12151c;
}

.shell {
  width: min(980px, calc(100vw - 32px));
  margin: 0 auto;
  padding: 28px 0;
}

.toolbar,
.controls {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  margin-bottom: 14px;
}

h1 {
  margin: 0;
  font-size: 28px;
  line-height: 1.1;
}

p {
  margin: 4px 0 0;
  color: #576071;
}

textarea,
pre {
  width: 100%;
  min-height: 180px;
  border: 1px solid #d4d9e2;
  border-radius: 8px;
  padding: 14px;
  font: 15px/1.5 ui-monospace, SFMono-Regular, Menlo, monospace;
  background: white;
}

pre {
  min-height: 260px;
  white-space: pre-wrap;
}

label {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  color: #333b49;
}

input,
select,
button {
  min-height: 36px;
  border: 1px solid #c7ced9;
  border-radius: 7px;
  padding: 0 10px;
  background: white;
  color: #12151c;
}

button {
  min-width: 96px;
  border-color: #171a22;
  background: #171a22;
  color: white;
  cursor: pointer;
}

button:disabled {
  opacity: 0.6;
  cursor: wait;
}

@media (max-width: 680px) {
  .toolbar,
  .controls {
    align-items: stretch;
    flex-direction: column;
  }

  label,
  input,
  select,
  button {
    width: 100%;
  }
}