fix success flash color contrast
fix success flash color contrast

closes CNVS-6675

previous green color didnt have enough contrast for WebAIM - WCAG

Change-Id: I36ae6eaddff0d622eb62e043709753893bed55e7
Reviewed-on: https://gerrit.instructure.com/32978
Tested-by: Jenkins <d95b56ce41a2e1ac4cecdd398defd7414407cc08@instructure.com>
Reviewed-by: Derek DeVries <ff87a0776152510efd53bb1f4ea089dbbc90e730@instructure.com>
QA-Review: Caleb Guanzon <54fa1f30d451e4f3c341a8f3c47c9215fd0be9c6@instructure.com>
Product-Review: Jason Madsen <bcb5fff571a20f07c35d17ba9c364855c776dce7@instructure.com>

ShreniiNepal/shrenii_lmp,va7map/canvas-lms,shidao-fm/canvas-lms,eCNAP/CANVAS,leftplusrightllc/canvas-lms,redconfetti/canvas-lms,venturehive/canvas-lms,snehakachroo1/LSI_replica,narigone/canvas,efrj/canvas-lms,instructure/canvas-lms,matematikk-mooc/canvas-lms,skmezanul/canvas-lms,dgynn/canvas-lms,efrj/canvas-lms,shidao-fm/canvas-lms,kyroskoh/canvas-lms,sfu/canvas-lms,matematikk-mooc/canvas-lms,jay3126/canvas-lms,SwinburneOnline/canvas-lms,skmezanul/canvas-lms,juoni/canvas-lms,HotChalk/canvas-lms,snehakachroo1/LSI_replica,instructure/canvas-lms,HotChalk/canvas-lms,snehakachroo1/LSI_replica,sdeleon28/canvas-lms,juoni/canvas-lms,grahamb/canvas-lms,kyroskoh/canvas-lms,wye0220/shindig-canvas,instructure/canvas-lms,wye0220/shindig-canvas,samuels410/greatlakes-lms,greyhwndz/canvas-lms,wrdsb/canvas-lms,sdeleon28/canvas-lms,efrj/canvas-lms,djbender/canvas-lms,whalejasmine/canvas-lms,Jyaasa/canvas-lms,Jyaasa/canvas-lms,usmschuck/canvas,djbender/canvas-lms,utkarshx/canvas-lms,roxolan/canvas-lms,utkarshx/canvas-lms,juoni/canvas-lms,antoniuslin/canvas-lms,sfu/canvas-lms,djbender/canvas-lms,Unow/canvas-lms,ShreniiNepal/shrenii_lmp,leftplusrightllc/canvas-lms,snehakachroo1/LSI_replica,wrdsb/canvas-lms,gbleydon/canvas-lms,tgroshon/canvas-lms,Jyaasa/canvas-lms,whalejasmine/canvas-lms,narigone/canvas,dgynn/canvas-lms,eCNAP/CANVAS,narigone/canvas,samuels410/greatlakes-lms,va7map/canvas-lms,jay3126/canvas-lms,AndranikMarkosyan/lms,AndranikMarkosyan/lms,matematikk-mooc/canvas-lms,antoniuslin/canvas-lms,instructure/canvas-lms,ShreniiNepal/shrenii_lmp,shidao-fm/canvas-lms,Rvor/canvas-lms,utkarshx/canvas-lms,va7map/canvas-lms,AndranikMarkosyan/lms,leftplusrightllc/canvas-lms,fronteerio/canvas-lms,roxolan/canvas-lms,jay3126/canvas-lms,shidao-fm/canvas-lms,skmezanul/canvas-lms,instructure/canvas-lms,HotChalk/canvas-lms,kyroskoh/canvas-lms,tgroshon/canvas-lms,grahamb/canvas-lms,dgynn/canvas-lms,gbleydon/canvas-lms,roxolan/canvas-lms,dgynn/canvas-lms,sfu/canvas-lms,SwinburneOnline/canvas-lms,fronteerio/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,antoniuslin/canvas-lms,SwinburneOnline/canvas-lms,efrj/canvas-lms,grahamb/canvas-lms,sdeleon28/canvas-lms,HotChalk/canvas-lms,utkarshx/canvas-lms,grahamb/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,djbender/canvas-lms,sdeleon28/canvas-lms,jay3126/canvas-lms,wrdsb/canvas-lms,va7map/canvas-lms,tgroshon/canvas-lms,matematikk-mooc/canvas-lms,tgroshon/canvas-lms,grahamb/canvas-lms,Unow/canvas-lms,gbleydon/canvas-lms,redconfetti/canvas-lms,usmschuck/canvas,venturehive/canvas-lms,Unow/canvas-lms,greyhwndz/canvas-lms,antoniuslin/canvas-lms,Jyaasa/canvas-lms,whalejasmine/canvas-lms,narigone/canvas,redconfetti/canvas-lms,fronteerio/canvas-lms,sfu/canvas-lms,whalejasmine/canvas-lms,kyroskoh/canvas-lms,usmschuck/canvas,samuels410/greatlakes-lms,venturehive/canvas-lms,venturehive/canvas-lms,Rvor/canvas-lms,ShreniiNepal/shrenii_lmp,redconfetti/canvas-lms,wye0220/shindig-canvas,skmezanul/canvas-lms,Rvor/canvas-lms,roxolan/canvas-lms,sfu/canvas-lms,AndranikMarkosyan/lms,eCNAP/CANVAS,greyhwndz/canvas-lms,juoni/canvas-lms,Rvor/canvas-lms,usmschuck/canvas,greyhwndz/canvas-lms,leftplusrightllc/canvas-lms,samuels410/greatlakes-lms,wrdsb/canvas-lms,fronteerio/canvas-lms,SwinburneOnline/canvas-lms,eCNAP/CANVAS