Update README.md

Author: aidanCQ

README.md

@@ -12,7 +12,7 @@ npm run build # Build component library with rollup.
 ``` 
 
 ### Design Tokens
-CSS variables are declared in `src/tokens.css`. Dark mode is enabled by the presence of the attribute `data-theme="dark"` higher up in the tree.
+CSS variables are declared in `src/tokens.css`. Dark mode is enabled when using the attribute `data-theme="dark"` higher up in the tree. See `src/tokens.css` for more details.