First, a big warning
This is NOT a feature for someone who isn't very technical. It requires you to understand how website code works. We can't provide support for custom code, so this is a use-at-your-own-risk feature.
Also, as Podpage evolves, we might change code on our site, that could cause custom code to break. This shouldn't happen that often (if ever) but it's something to be aware of.
Customizing the page
On your custom page edit page in the Podpage Dashboard, click the <> button. This will open the code editor, where you can add whatever HTML you want.
You can add CSS that will only be active on this specific custom page in the Custom CSS Code field of the Custom Page editor in the Dashboard.
The CSS code will be the last CSS loaded on the page, so you can overwrite other styles.