We do not provide support for hacks, so use them at your own risk. If you're not comfortable with coding, we recommend against using this workaround.
By default, there is not a way to customize or style the 404 page of Semplice without modifying theme files. However, you can use a simple plugin to make any page in Semplice serve as your 404 page.
Once you've created and published the page in Semplice, follow these steps to set the page as a 404 page for your site.
Step 1: Download & install the '404page' plugin
Download the '404page' WordPress plugin here or go to Plugins > Add New in Wordpress and search for it. Install and activate the plugin.
Step 2: Set the 404 page
In WordPress, navigate to Appearance > 404 Error Page. Under 'Page to be displayed as 404 page', set the 404 page you created in Semplice. Make sure 'Activate Compatibility Mode' is enabled in the options.
Note: If you do not see your page in the list, make sure it is published and not set to draft.
That's it! Now, anytime someone lands on a broken link or incorrect URL for your site, your custom 404 page will be displayed.