Color contrast - Outcomes

CNVS-15581

Two small UI tweaks to increase foreground-
background contrast in the Outcomes section.

IMPORTANT: This ticket is only for the high-
contrast UI. To enable the high-contrast UI, go
to Settings then scroll down and make sure
"Use High Contrast Styles" is set to ON.

Test plan:
- Refer to the image I attached in JIRA with the
  fixes circled in red.
- Enable high contrast UI in Canvas (see above)
- Go through each issue Nathan entered into the
  JIRA and compare with the updated UI to make
  sure it's fixed.
- The webAIM color contrast tester can be found
  here: http://webaim.org/resources/contrastchecker/

Change-Id: I6bfe367dbec27db373ceba582dc04032cbe90ae9
Reviewed-on: https://gerrit.instructure.com/42096
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Vincent Gonzalez <vgonzalez@instructure.com>
QA-Review: Anna Koalenz <akoalenz@instructure.com>
Product-Review: Chris Hart <chart@instructure.com>