Part 3 - Adding the .post-enter-started class

Post.js

executeEnteringTransition = (node, done) => {
  this.postStyler.set({ ...this.from, visibility: 'visible' });
  node.classList.add('post-enter-started'); // add this line
  
  /* same code */
  
 complete: () => {
    node.classList.remove('post-enter-started'); // add this line
    done();
  }
}