adjust style on total grade column tooltips
adjust style on total grade column tooltips

refs CNVS-38346

test plan:
* ensure Jenkins passes

Change-Id: I61692d3c9f14a10f32164b849e48ed011da788b2
Reviewed-on: https://gerrit.instructure.com/120971
Tested-by: Jenkins
Reviewed-by: Brian Park <760e7dab2836853c63805033e514668301fa9c47@siimpl.io>
Reviewed-by: Gary Mei <4dff5ebcff9ed76793b70b9470ac64791a16ed11@instructure.com>
Product-Review: Jeremy Neander <20252aad5efdc666f083d82ab63ed0f9f72a043e@instructure.com>
QA-Review: Jeremy Neander <20252aad5efdc666f083d82ab63ed0f9f72a043e@instructure.com>

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