not all corners are rounded in the Mint-Y theme

I've just finished reading the new blog post for May and noticed from the screenshots that when it mentions that not Mint-Y has slightly rounded corners, not all of the corners are round:

<img width="821" height="714" alt="Image" src="https://github.com/user-attachments/assets/133124f0-bd91-49a1-88e3-f1e193338736" />