Code blocks not rendered properly in smaller screens

I noticed an issue in which the code block in the "git log --oneline improvements" section renders badly in smaller screen. Further it also breaks the single-pagedness of the website. As a consequence, one might have to zoom in to read the post and scrolling might take you to empty space in the right. Screen shots:

• Desktop view:
  

• Mobile view (iPhone SE resolution)
  

  

  Note the scroll bar in the bottom of the page.

It would be nice to fix this by making the code blocks render in such a way that the code within the block is scrollable rather than the whole page being scrollable.

Note: Initially mentioned in https://github.com/git/git.github.io/pull/366#issuecomment-471316738

Beginne mit dem Abschnitt “git log --oneline improvements” auf der verlinkten Git Developer Pages-Website und bilde das Layout bei der in den Screenshots gezeigten iPhone-SE-Auflösung nach. Untersuche die responsiven Styles, die Codeblöcke beeinflussen; fertig ist es, wenn der Code selbst horizontal scrollt, ohne einen seitenweiten Überlauf oder leeren Raum zu erzeugen.