Some more basic plots with Plots.jl for illustrating calculous and linear algebra books, but can we write better plotting codes?

I started re-making the plots to illustrate some mathematical ideas. The repo is for illustrating the basic ideas through easily created plots and animations and the use and tuning of parameters of Plots.jl
This is less ambigous than to create a package.
The problem seems to be that there is no one recommended way to write plotting codes “elegantly” (does any visualization book reinforces that apart from Grammar of Graphics?), and most blocks of codes turn out to be quick and dirty works – but they worked and created surprising results. I am looking forward to some critiques and advises to make the code more readable and organized. Thx

By the way, the repo is open-sourced so usage of these illustrations is permitted with some citing.