fix(browser-repl): use an error background color that makes syntax highlighting legible COMPASS-8308

[djechlin-mongodb]

These changes are requested by design:

1. The light red background should remain the darker background.
2. The initial error declaration should be light red not dark red.
3. The first line of the error, and the initial text, should be white.
4. There should be a light red indent bar (in css, a left border) to the left of the stack.

New, better:

Old, worse: