The previous commits broke support on Chrome / Safari on iOS.
`HTMLElement.scroll` does not seem to work when the height is set
as a percentage. This commit also uses `HTMLElement#scrollHeight`
instead of "offsetHeight".
I bought a new laptop recently, and I discovered that I couldn't view
a surah without a vertical scroll bar. The timer for an ayah wasn't
visible without scrolling. This change will hopefully address that.