Navigation sticky box with anchor links and highlight

I’m building my site locally and there are long pages, in which I would like to put a sticky box containing the titles of the paragraphs/sectiones, so that it will be easy to navigate through the page:

• by clicking on one of the title in the box, the page will scroll to the corresponding section;
• moreover, the section currently showing will be highlighted in the box, in this way is easy to understand which section is showing even when the title of the section is not showing in the page.

The result is something like this.

How hard is to achieve it without installing any plugins and/or themes, but just by working with the style.css and other files? If it is too hard, are there any plugin which can help?

I searched a lot here and on other sites, but I mainly found how to achieve this with the main menu, not with an independent box.

What is a good starting point?