Creating My Own Sign in Page

I’m wondering how do I change the length of a form container because I wish it was skinnier because it is too wide

You can create a custom form with Text Entries inside a small Container and include a button to faux submit or to add a row to a different table.

Never Mind, How can we customize the boring sign in form? Not the welcome screen but the normal screen.

You cant at the moment.

But how can I make my own sign-in page and sign up page.