I'll make an example with the Acme.BookStore project and modify the login page of the ABP Commercial MVC
template.
To replace a view/CSS with a new one, rename your new file as the original one and put it in the same directory with the original directory path.
For this example, I'll overwrite Account/Login
page.
Below is the content of my customized login view.
Create a file named Default.cshtml and put it in the folder *Acme.BookStore\src\Acme.BookStore.Web\Themes\Lepton\Layouts\Account*