improvements to styles and implementations

[tonyfast]

• flex to style main body
• more direct toc implementation
• better landmark descriptions

[github-actions]

A preview fo the exported examples will be rendered at
https://deathbeds.github.io/nbconvert-a11y/branch/bulk-improve/exports/html/lorenz-executed-a11y.html

[tonyfast]

@sgkane gave feedback that she'd like more font options. this has been implemented and can be tested at https://tonyfast.github.io/tonyfast/draft/tonyfast/tonyfast/tonyfast/xxiv/2024-02-20-multiindex-html.html

i've also moved the settings to the top so it easier to access

[tonyfast]

the describedby technique on the main element was very chatty on voiceover and i hope removing fixes that.

[tonyfast]

adding extremely large font sizes causes some reflow/overflow challenges in the UI.

we're adding an option to remove overflow/wrapping so that digital magnifier users can benefit from following a single line of text rather than carriage returning on a wrapped representation