html, body { margin: 0; height: 100%; }
body {
  display: flex;
  flex-direction: column;
  background: #12161c;
  color: #d7e2ee;
  font: 14px/1.45 ui-monospace, Consolas, monospace;
}
header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 0.65rem 1rem;
  border-bottom: 1px solid #243040;
  color: #7ec8e3;
}
.btns { display: flex; gap: 0.4rem; }
button {
  font: inherit;
  background: #243040;
  color: #d7e2ee;
  border: 0;
  padding: 0.35rem 0.7rem;
  cursor: pointer;
}
#pretty { background: #7ec8e3; color: #12161c; }
textarea {
  flex: 1;
  width: 100%;
  border: 0;
  resize: none;
  background: transparent;
  color: inherit;
  font: inherit;
  padding: 1rem;
  outline: none;
}
#err {
  margin: 0;
  padding: 0.45rem 1rem;
  background: #3a1c1c;
  color: #ef9a8a;
}
#err[hidden] { display: none; }