Modernize Bootstrap Sass: Migrate from @import to @use/@forward syntax

[seuros]

This is my first attempt to give back to the community since I've been using OPNsense for nearly a decade. My router recently grew its own consciousness and told me to either contribute or get a license. So here is the Bootstrap upgrade I extracted from my port for the Greater Firewall of North Korea.

Technical Details

This upgrade removes the deprecated @import statements that were causing circular dependency nightmares and replaces them with the modern Sass module system (@use and @forward).

Why this matters:

• Future Dart Sass 3.0.0 compatibility: The @import rule will be removed entirely in Dart Sass 3.0.0 (expected no sooner than October 2026). Without this migration, OPNsense themes will stop compiling when that version is released
• Already deprecated: As of Dart Sass 1.80.0 (October 2024), @import is officially deprecated and throws warnings
• Eliminates circular dependencies: The old @import system would eagerly load everything, causing variables to leak globally and creating a tangled web of dependencies
• Namespace isolation: With @use, each file's variables and mixins are properly encapsulated, preventing naming collisions
• Performance improvements: Files are only loaded once with @use, unlike @import which would reload files multiple times
• Cleaner variable scope: No more !global flags needed - everything stays properly scoped

Changes Made

• Migrated 118 SCSS files across both themes (opnsense and opnsense-dark)
• Replaced deprecated color functions:
  • lighten()/darken() → color.adjust()
  • red()/green()/blue() → color.change()
  • Global percentage/floor functions → math.percentage()/math.floor()
• Fixed undefined variable/mixin errors by adding proper @use declarations
• Added !optional flags to @extend statements to prevent compilation errors
• Cleaned up trailing whitespace for good measure

Testing

Both themes compile successfully with only minor mixed-declarations warnings (future CSS cascade layer behavior, not critical):

✅ opnsense theme compiles
✅ opnsense-dark theme compiles
✅ All deprecation warnings eliminated (except mixed-decls which is informational)

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P.S. Kidding about North Korea, it was Syria or Russia. Don't remember, I was offline firewalled behind OPNsense.

[AdSchellevis]

@seuros thank your for spending time on the theme package, as this is quite a large blob of changes, I'm not sure yet when we can process these.

Eventually it looks like we should deprecate the @import statements (https://sass-lang.com/blog/import-is-deprecated/) and changing the default bootstrap files is likely much easier than aiming for an upgrade anyway.

[seuros]

Thank you for reviewing! I completely understand .
it is indeed a large changeset to review all at once.

I've actually been maintaining these changes locally for a while now, but having to reapply them after every OPNsense upgrade has become routine. So I figured it's time to contribute it upstream!

The changes are entirely mechanical, no functional changes to the generated CSS, just modernizing the Sass syntax to use @use/@forward.
This makes the Bootstrap code more maintainable with proper namespacing.

I'd be happy to also migrate all the plugin themes in the
opnsense/plugins repository:

• theme-cicada
• theme-rebellion
• theme-tukan
• theme-vicuna
• theme-advanced

If I migrate all the official themes, there's will be no extra work to be done, everything will just work and the deprecation warnings will be gone. I can submit a separate PR to the plugins repo once this is accepted. What i do is to use the migrator and check manually each page that get affected.

I'm happy to:

• Break this into smaller PRs if that would help review
• Help test against any specific scenarios you're concerned about

No rush on my end.
I know you have priorities. Just wanted to stop maintaining my own fork after using OPNsense for almost a decade!

PS: the reason i put 1 PR/commit. is that in case there is some unseen regression, you just revert. But this is just CSS compilation, nothing is active here.

[AdSchellevis]

no need to break it up, I just need some time to test and assess impact, I do compile these regularly, so I need to know for sure the output remains the same, that's all.

The plugins are not maintained by the core team, so before spending time, I would advise to ask the maintainers when this is merged.

Out of sheer curiosity, why would you like to compile our theme every release?

[seuros]

Good question! I don't recompile every release - just major releases. This time it's for the newly released Viper.

Over the years, I've built quite a few custom plugins on top of OPNsense (LoRa emergency messaging, 4G failover, custom UPS integration for older hardware that doesn't support NUT, etc.). Some of these actually conflict with OPNsense's enterprise offerings, and they're all highly optimized for my specific hardware setup.

I also have a custom dashboard theme with full WebGL 3D network representation, heatmaps, etc. - but that breaks compatibility with non-Chrome browsers and mobile, so not very general-purpose.

I'm not interested in open-sourcing most of these custom tools because:

1. They'd require ongoing support I'm not willing to provide
2. People would expect free solutions with enterprise-level support
3. They're more like custom scripts for specific hardware than general-purpose modules

I also make other customizations like removing legacy DHCP and aliasing everything to KEA.

But the Bootstrap/Sass migration is different - it's not a custom feature, it's a general improvement that everyone will need eventually. The deprecation warnings affect all OPNsense installations, and Dart Sass 3.0 will break compilation entirely.

That's why I'm contributing this specific fix upstream rather than keeping it in my private fork!