fixes calendar x icon hiding on small screens
fixes calendar x icon hiding on small screens

fixes the calendar modal being cut off when the browser
window is really small.

fixes CNVS-21755

test plan:
- From within the calendar create a new calendar event via the "+" icon
- Under the edit event field select the "more options" button
- Give the event a title and under the content editor add 20 lines (can be single character, just hit 'enter' after each one)
- Select "Update Event"
- Click the newly created event.
- Note that the top of popover (and the 'X' to close it) is positioned onscreen
- Enlarge and shrink the window notice x and title stay on screen

Change-Id: I37700ac74742ecd3ad27692a6e5393c21f7bf83a
Reviewed-on: https://gerrit.instructure.com/60328
Reviewed-by: Jennifer Stern <7e594e5cba47371ac9ee694a84b9d94f9f6ec815@instructure.com>
Tested-by: Jenkins
QA-Review: Steven Shepherd <e794458448443812fb2685675aab3bbd1a3891bc@instructure.com>
Product-Review: Matthew Wheeler <ce71fbafda91d6c8f12582e1837687d5fe592dd9@instructure.com>

sfu/canvas-lms,sfu/canvas-lms,AndranikMarkosyan/lms,fronteerio/canvas-lms,dgynn/canvas-lms,jay3126/canvas-lms,fronteerio/canvas-lms,fronteerio/canvas-lms,grahamb/canvas-lms,instructure/canvas-lms,venturehive/canvas-lms,matematikk-mooc/canvas-lms,venturehive/canvas-lms,AndranikMarkosyan/lms,leftplusrightllc/canvas-lms,leftplusrightllc/canvas-lms,instructure/canvas-lms,HotChalk/canvas-lms,roxolan/canvas-lms,roxolan/canvas-lms,narigone/canvas,djbender/canvas-lms,roxolan/canvas-lms,sfu/canvas-lms,SwinburneOnline/canvas-lms,narigone/canvas,snehakachroo1/LSI_replica,leftplusrightllc/canvas-lms,redconfetti/canvas-lms,sfu/canvas-lms,roxolan/canvas-lms,kyroskoh/canvas-lms,instructure/canvas-lms,dgynn/canvas-lms,HotChalk/canvas-lms,instructure/canvas-lms,grahamb/canvas-lms,SwinburneOnline/canvas-lms,SwinburneOnline/canvas-lms,grahamb/canvas-lms,redconfetti/canvas-lms,matematikk-mooc/canvas-lms,matematikk-mooc/canvas-lms,venturehive/canvas-lms,instructure/canvas-lms,AndranikMarkosyan/lms,jay3126/canvas-lms,instructure/canvas-lms,redconfetti/canvas-lms,HotChalk/canvas-lms,djbender/canvas-lms,HotChalk/canvas-lms,jay3126/canvas-lms,matematikk-mooc/canvas-lms,grahamb/canvas-lms,djbender/canvas-lms,sfu/canvas-lms,grahamb/canvas-lms,kyroskoh/canvas-lms,kyroskoh/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,snehakachroo1/LSI_replica,narigone/canvas,narigone/canvas,fronteerio/canvas-lms,jay3126/canvas-lms,dgynn/canvas-lms,SwinburneOnline/canvas-lms,djbender/canvas-lms,leftplusrightllc/canvas-lms,kyroskoh/canvas-lms,redconfetti/canvas-lms,venturehive/canvas-lms,dgynn/canvas-lms,snehakachroo1/LSI_replica,snehakachroo1/LSI_replica,AndranikMarkosyan/lms