In Zoomforth, you can make a Style Preset to create different elements for tiles and sections. Different design elements of a tile and text section can be customized as you create or modify a style preset. You can change the font transparency, margin, heading style line height, or tile border. Style presets permit users to apply specific styles to selected tiles without recreating or duplicating the style every time you create a site.
One thing you can do in a style preset is to create a border for your tiles.
Adding / customizing tile / text section border via style preset:
Navigate to edit the theme from the target site.
In the theme editor, navigate to edit an existing style preset already applied to the target tile / text section, or create a style preset. If you are to create a new style preset, you have to apply the new style preset to the target tile / text section later.
Click Tiles, and look for the Border field from the style preset editing interface, on the left pane.
Set the value of the border using this format: <border-width> <style> <color> (e.g. 2px solid #000).
Apply the style preset to the target tile or text section.
For more information regarding Style Presets, you can check this article.