How to add .html code to your pages using code element:

1)Under the "Site" Menu, on left hand side of the builder

2) Select "Pages"

3) Double click on the page you wish to add the code to

4) Click "Elements" on the right hand side of the screen

5) Click "+" button at the bottom of the screen

6) Hover over "content" select "code"

7) Here you can add the code directly

Make sure to publish after completing your changes.