Update Saas and Vite to fix deprecation warnings

This commit updates Dart Sass to version 1.79.4 to address deprecation
warnings. It also updates Vite to 5.4.x to be able to use the modern
Sass compiler.

Changes:

- Update `saas` to latest
- Update `vite` from 5.3.x to 5.4.x
- Replace `lighten` and `darken` with `color.adjust` due
  to deprecation.
- Set Vite to use the modern compiler instead of the deprecated legacy
  one
- Pin `sass` to patch versions to prevent unexpected deprecations using
  tilde (~) for in package.json.

package.json

@@ -75,12 +75,12 @@
     "remark-lint-no-dead-urls": "^2.0.0",
     "remark-preset-lint-consistent": "^6.0.0",
     "remark-validate-links": "^13.0.1",
-    "sass": "^1.77.8",
+    "sass": "~1.79.4",
     "start-server-and-test": "^2.0.4",
     "terser": "^5.31.3",
     "tslib": "^2.6.3",
     "typescript": "~5.5.4",
-    "vite": "^5.3.4",
+    "vite": "^5.4.8",
     "vitest": "^2.0.3",
     "vue-tsc": "^2.0.26",
     "yaml-lint": "^1.7.0"