strapi/packages/strapi-helper-plugin/lib/src/components/Wysiwyg/styles.scss

.editorWrapper {
  min-height: 350px;
  margin-top: .9rem;
  padding: 8px 10px 0 10px;
  border: 1px solid #E3E9F3;
  border-radius: 0.25rem;
  line-height: 18px;
  font-size: 13px;
  box-shadow: 0px 1px 1px rgba(104, 118, 142, 0.05);
}

.editorFocus {
  border-color: #78caff;
}

.editorInput {
  height: 0;
  width: 0;
}