fix: lepton theme customization

Author: sumeyyeKurtulus

docs/en/ui-themes/lepton/customizing-lepton-theme.md

@@ -45,9 +45,16 @@ export const appConfig: ApplicationConfig = {
 
 Import your style file to `src/style.scss`
 
-```css
+```scss
+/* style.scss */
+@import 'your-custom-style';
+```
+
+or
+
+```scss
 /* style.scss */
-import 'your-custom-style';
+@use 'your-custom-style';
 ```
 
 Or add your style file to the `styles` arrays which in `angular.json` file