(chore) Modernize the codebase just a bit (#2894)
(chore) Modernize the codebase just a bit (#2894)

* (chore) every browser but VERY old IE has `forEach` on query results now
* (chore) use more modern classList DOM API
  - All browsers we support now support this API.
highlightjs/highlight.js,highlightjs/highlight.js,isagalaev/highlight.js,carlokok/highlight.js,isagalaev/highlight.js,highlightjs/highlight.js,highlightjs/highlight.js,carlokok/highlight.js,carlokok/highlight.js,carlokok/highlight.js