body {
  font-family: system-ui, -apple-system, Segoe UI, Roboto, Ubuntu, Cantarell, Noto Sans, Arial, sans-serif;
  background: #f1f5f9;
  min-height: 100vh;
  display: grid; place-items: center;
  margin: 0;
}
.wrap { text-align: center; padding: 2rem; }
h1 { font-size: 1.6rem; margin-bottom: 1.2rem; }
.otp { display: flex; gap: 1rem; justify-content: center; }
.otp-input {
  width: 60px; height: 70px;
  border: none;
  border-bottom: 4px solid black;  /* negro por defecto */
  background: transparent;
  font-size: 2rem;
  text-align: center;
  outline: none;
  transition: border-color .2s;
}
.otp-input.filled { border-color: green; } /* verde cuando tiene valor */
.debug {
  margin-top: 1rem;
  background: #0f172a; color: #e2e8f0;
  padding: .5rem 1rem; border-radius: .5rem;
  font-family: ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
}