Generated by SassMeister.com.

input.scss

// This is in custom theme
$colorMain: red;
// $colorSec: blue;
// $colorSec: $colorMain;

// This in default theme

$colorMain: #0af !default; // Allow to override color from other theme
$colorMain: var(--user-brandPrimary500, $colorMain);

$colorSec: $colorMain !default; // Allow to override color from other theme
$colorSec: var(--user-theme-secondaryColor, $colorSec);

a {
    color: $colorMain;
    color: $colorSec;
}

output.css

a {
  color: var(--user-brandPrimary500, red);
  color: var(--user-theme-secondaryColor, var(--user-brandPrimary500, red));
}

settings.json

{
  "sass": {
    "compiler": "dart-sass/1.32.12",
    "extensions": {},
    "syntax": "SCSS",
    "outputStyle": "expanded"
  },
  "autoprefixer": false
}