The GreaseMonkey script bitbucket.user.js modifies display styles for
BitBucket.  Currently, the following changes are applied:

1.  Code highlight div gets a black background, and the default text
    color is changed to SpringGreen.

2.  The diff output uses a black background with SpringGreen default
    text.  Insertions use yellow text, deletions red text.  The
    deleted or inserted code gets a dark gray background.

Licensed very permissively under the OWL: