Fix client issues that interfere with strict CSP policies

## Bug report form

### Steps to reproduce
1. Go to https://qa.hypothes.is/docs/help
2. Check console for CSP errors

### Expected behaviour
No CSP errors.

### Actual behaviour
CSP errors are triggered by:

1. Inline styles inserted into the host page by `adder.js`
2. Inline styles inserted into app.html when rendering LaTeX markup using KaTeX.

Reproduce the CSP errors at https://qa.hypothes.is/docs/help and inspect the inline styles inserted by adder.js and app.html when KaTeX renders LaTeX. Trace both sources and verify completion by confirming that the page renders without CSP errors under the strict policy.

Written by the indexing model from the issue text.