Sass deprecation warnings on site build

[irby]

Issue Description

We are seeing some SASS deprecation notices when building the site code (link). Would be a good idea to address these warnings while they're still just warnings.

How to Reproduce

• Run yarn build while on the root directory

   ╷
54 │   $dividend: abs($dividend);
   │              ^^^^^^^^^^^^^^
   ╵
    node_modules/bootstrap/scss/vendor/_rfs.scss 54:14             divide()
    node_modules/bootstrap/scss/mixins/_grid.scss 66:15            row-cols()
    node_modules/bootstrap/scss/mixins/_grid-framework.scss 43:13  @content
    node_modules/bootstrap/scss/mixins/_breakpoints.scss 65:5      media-breakpoint-up()
    node_modules/bootstrap/scss/mixins/_grid-framework.scss 32:5   make-grid-columns()
    node_modules/bootstrap/scss/_grid.scss 72:3                    @import
    node_modules/bootstrap/scss/bootstrap.scss 16:9                @import
    resources/sass/app.scss 10:9                                   root stylesheet

Deprecation Warning: Sass's behavior for declarations that appear after nested
rules will be changing to match the behavior specified by CSS in an upcoming
version. To keep the existing behavior, move the declaration above the nested
rule. To opt into the new behavior, wrap the declaration in `& {}`.

[allella]

Closing this since we agreed in #451 to keep updating Sass and ignore warnings.

We plan to eventually upgrade Bootstrap or move to another CSS framework in #252 so we don't need to spend time on this when that work should resolve it.