Handle Sass deprecation warnings

[Not-A-Normal-Robot]

Currently there are two to worry about:
https://sass-lang.com/documentation/breaking-changes/color-functions/
https://sass-lang.com/documentation/breaking-changes/legacy-js-api/

Deprecation Warning: darken() is deprecated. Suggestions:           8:49:12 PM

color.scale($color, $lightness: -69.1525423729%)
color.adjust($color, $lightness: -40%)

More info: https://sass-lang.com/d/color-functions

    ╷
196 │         background-color: darken(colors.$secondary-color-alpha75, 40%);
    │                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    ╵
    components/header.vue 196:27  root stylesheet
Deprecation Warning: darken() is deprecated. Suggestions:           8:49:12 PM

color.scale($color, $lightness: -62.5830508475%)
color.adjust($color, $lightness: -36.2%)

More info: https://sass-lang.com/d/color-functions

    ╷
265 │         background-color: darken(colors.$secondary-color-alpha50, 36.2%);
    │                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    ╵
    components/header.vue 265:27  root stylesheet