Error: compound selectors may no longer be extended is encountered when building the themes

Issue

When creating the bare-bone theme without any customization, the build is encountered with the below error:

[14:26:26] 'build:compile-css' errored after 4.9 s
[14:26:26] Error in plugin "sass"
Message:
    build/_css/compat/components/_dropdowns.scss
Error: compound selectors may no longer be extended.
Consider `@extend .dropdown-item, .disabled` instead.
See http://bit.ly/ExtendCompound for details.

   ╷
34 │         @extend .dropdown-item.disabled;
   │                 ^^^^^^^^^^^^^^^^^^^^^^^
   ╵
  build/_css/compat/components/_dropdowns.scss 34:11  root stylesheet
Details:
    formatted: Error: compound selectors may no longer be extended.
Consider `@extend .dropdown-item, .disabled` instead.
See http://bit.ly/ExtendCompound for details.

   ╷
34 │         @extend .dropdown-item.disabled;
   │                 ^^^^^^^^^^^^^^^^^^^^^^^
   ╵
  build/_css/compat/components/_dropdowns.scss 34:11  root stylesheet
    line: 34
    column: 11
    file: /Users/jordi/Downloads/Liferay/test1-theme/build/_css/compat/components/_dropdowns.scss
    status: 1
    messageFormatted: build/_css/compat/components/_dropdowns.scss
Error: compound selectors may no longer be extended.
Consider `@extend .dropdown-item, .disabled` instead.
See http://bit.ly/ExtendCompound for details.

   ╷
34 │         @extend .dropdown-item.disabled;
   │                 ^^^^^^^^^^^^^^^^^^^^^^^
   ╵
  build/_css/compat/components/_dropdowns.scss 34:11  root stylesheet
    messageOriginal: compound selectors may no longer be extended.
Consider `@extend .dropdown-item, .disabled` instead.
See http://bit.ly/ExtendCompound for details.

   ╷
34 │         @extend .dropdown-item.disabled;
   │                 ^^^^^^^^^^^^^^^^^^^^^^^
   ╵
  build/_css/compat/components/_dropdowns.scss 34:11  root stylesheet
    relativePath: build/_css/compat/components/_dropdowns.scss
    domainEmitter: [object Object]
    domainThrown: false

[14:26:26] 'build' errored after 5.96 s

Environment

Liferay DXP 7.3
node -v 14.17.0
npm -v 6.14.13

Resolution

The js-themes-toolkit switched the pre-processor from Libsass to Dart Sass. And, Dart Sass has introduced some breaking changes that cause builds of older themes to fail.
To build the themes, disable the Dart Sass in the configuration file to keep going to use the current basic tooling.
package.json:
```
	"liferayTheme": {
		"sassOptions": {
			"dartSass": false
		},
		//...
	},
```

Error: compound selectors may no longer be extended is encountered when building the themes

Issue

Environment

Resolution

Additional Information