The colour scheme is really good, neat and simple. really good.
But the layout is broken! even in tabs and small screens, this is not good!
Look what I got from mobile:
Same, for the tabs and even desktops, the code sections breaks the layout, check:
Too much padding at the left!, content goes off the page! please fix.
Also there is no scrollbar, this is so bad!
I like the hover animation over the left links, cool. They come with a simple icon too, very good. I suggest you may make the animation a little faster.
allow the user hide/show the left navigation panel using a button for instance. The space could be used for reading panel too.
This could be great if you could keep the left link active, when users is reading the related data. for example as a user is reading CSS section, you keep the CSS link at the left active, same when it scrolls to next section, next links gets activated then.
Keep going on great work, happy programming