Hello.How can i use CSS to manually alter the star color，I want to know where I should put the code?
You should be able to set the star color in the app settings here: https://judge.me/settings?jump_to=widget+star+color
Under Review Widget > Widget Header > it should be the first option:
Alternatively, if you just want to use CSS, you would place it on the Main CSS file for your theme in Shopify. Typically theme.scss.liquid, or if your platform is Woocommerce, in your wordpress admin under Appearance > Customize > Custom CSS - Place it here.
You may need to use an !Important tag to overwrite the CSS from our application. Let me know if this was clear or if you have further questions. Thank you!