laws special emphasis background color

[jamesdbrock]

In places in the text where there are laws, the book uses a special background color 99ddcc. Can we set background color in JupyterLab? I've marked laws as **`law`**

For functions or types mentioned for the first time, there is also a special background color. I've marked those locations (and some other too, need to disambiguate) as __`fn`__