Replace @import with @use for theme styles

This commit addresses issue #2781 by migrating from deprecated @import statements to the modern @use directive in color-modes/index.scss.

Changes:
- Replaced all @import statements with @use
- This removes Sass deprecation warnings
- Follows Sass module system best practices

Author: prashant2007-wq

src/color-modes/index.scss

@@ -1,11 +1,11 @@
 // All themes
 
-@import './themes/light.scss';
-@import './themes/light_colorblind.scss';
-@import './themes/light_high_contrast.scss';
-@import './themes/light_tritanopia.scss';
-@import './themes/dark.scss';
-@import './themes/dark_dimmed.scss';
-@import './themes/dark_high_contrast.scss';
-@import './themes/dark_colorblind.scss';
-@import './themes/dark_tritanopia.scss';
+@use './themes/light.scss';
+@use './themes/light_colorblind.scss';
+@use './themes/light_high_contrast.scss';
+@use './themes/light_tritanopia.scss';
+@use './themes/dark.scss';
+@use './themes/dark_dimmed.scss';
+@use './themes/dark_high_contrast.scss';
+@use './themes/dark_colorblind.scss';
+@use './themes/dark_tritanopia.scss';