CSS issue: Icons are box in Linux Production

[diligentwing]

CSS Icons issue
Icons are square box in linux production.

The make-container-max-widths mixin has been deprecated as of v4.5.2. It will be removed entirely in v5.
on line 8:5 of ../lib/bootstrap/scss/mixins/_deprecate.scss, in mixin deprecate
from line 35:12 of ../lib/bootstrap/scss/mixins/_grid.scss, in mixin make-container-max-widths
from line 89:22 of ../Themes/flexblack/_layout.scss
from line 119:9 of ../Themes/flexblack/theme.scss