I studied HTML/CSS/JS at least once through books or lectures. However, most of them were not pure(?), but jQuery and Bootstrap were added in abundance, and the layout was organized using old grammar like float, so all the information was a mess. When I first listened to the lecture, I was disappointed because I thought it was just a summary of the contents in the book... But when I actually created a page, I realized how well the lecture was made and reflected on it. In particular, the mouse clicks, touch events, etc. at the end of the last part, most other lectures teach you using plugins and end it! It was great that I could implement it with pure JavaScript. I should study more by repeating the exercises I did here as a basic base.