A&R Sass @import deprecation

#### Description:

Currently, there is a warning showing in builds due to the @ import deprecation (https://sass-lang.com/blog/import-is-deprecated/).

We are unsure if they will make it mandatory in Angular 20. Solution is to convert from the use of @ import or we completely move away from SASS and go to plain CSS.

#### Acceptance Criteria:
[Note: Use 'Given/When/Then' format if it makes sense to. Otherwise, a simple checklist that can be tested.]

#### Development Checklist:

- [ ] Updating style code accordingly so there are no more warnings
- [ ] Ensure no warnings exist related to styles on frontend

#### Dependencies

- Blocked by [112](https://github.com/orgs/bcgov/projects/49/views/1?filterQuery=bootstrap&pane=issue&itemId=94471607&issue=bcgov%7Creserve-rec-public%7C112)
- Blocking
- Related to [#575](https://github.com/bcgov/parks-data-register/issues/575) and https://github.com/bcgov/parks-reso-public/issues/512

**Relevant documentation as reference**

**Definition of Ready**

- [ ] Acceptance criteria are included
- [ ] Wireframes are included (if applicable)
- [ ] Design / Solution is accepted by Product Owner (if applicable)
- [ ] Dependencies are identified (technical, business, regulatory/policy)
- [ ] Story has been estimated (under 13 pts)

**Definition of Done**
- In progress:
- [ ] Acceptance criteria are tested (Functionality meets the acceptance criteria defined in the ticket)
- [ ] UI meets accessibility requirements
- [ ] Unit tests are written
- [ ] Work is traceable in GitHub
- [ ] PR linked to ticket number
- [ ] If needed/required - Dev adds flag/label to highlight any migration steps necessary prior to PROD deployment
- Code review:
- [ ] Code is peer reviewed and has passed CI/CD tests
- QA:
- [ ] Acceptance criteria are tested (Functionality meets the acceptance criteria defined in the ticket)
- [ ] Code is potentially shippable to the production environment
- [ ] Functional features have been tested and passed by QA
- [ ] UI components tested by designer
- [ ] Code is deployed to PROD when moved to 'done' column (unless requested otherwise by PO)
- PO Review:
- [ ] Acceptance criteria are tested (Functionality meets the acceptance criteria defined in the ticket)
- [ ] Reviewed and approved by Product Owner

#### Notes:
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Start by locating the frontend Sass styles and running the frontend build to reproduce the deprecation warning. Review the dependency on issue #112 before choosing between converting imports and moving to plain CSS; done means the frontend build has no style-related warnings.

Written by the indexing model from the issue text.