@wordpress/block-library/build-style/form-input/editor.css

Block library for the WordPress editor.

.wp-block-form-input .is-input-hidden {
  display: flex;
  position: relative;
  font-size: 0.85em;
  opacity: 0.3;
  border: 1px dashed;
  padding: 0.5em;
  box-sizing: border-box;
  background: repeating-linear-gradient(45deg, transparent, transparent 5px, currentColor 5px, currentColor 6px);
  justify-content: center;
  align-items: center;
}
.wp-block-form-input .is-input-hidden::after {
  content: attr(data-message);
}
.wp-block-form-input.is-selected .is-input-hidden {
  opacity: 1;
  background: none;
}