VideoPsalm enables to define the style attributes of the slides globally, and/or individually.

Usually, you will want all slides to use the same font, font size, font colors and background.

In this case, adjust the style attributes at the "Base" or "Songbooks" style level.

For a specific song, you may want to set a specific background, or font size. These style attributes will then "override" the "Base" style attributes.

Can there be a global background or must it be defined for each slide? Or each song verse?

The global background is the one assigned to the "Base" (or "Songbooks") style level.

When you assign another background to a song verse, this specific song verse will be displayed with this specific background.

To learn more about cascading styles, follow the links at the bottom of my answer.

Is there such a thing as a Theme like OpenLp?

No. VideoPsalm uses cascading styles.

Could a theme, or themes be imported from OpenLp?

Yes: VideoPsalm -> Top toolbar -> "Background" tab -> "Image" gallery drop down -> Import images (at the bottom) -> Follow the instructions.

Add beautiful images and video loops for free from the internet

VideoPsalm cascading styles

VideoPsalm uses the concept of cascading style attributes, enabling you to define any style attribute at any level : song verse, song, songbook, all songbooks, base.

Please let me know if the following article explains well enough how to make best use of cascading styles:

How to change the background of a song or a whole songbook - Cascading styles part one

How to assign a background to a song verse or to the whole song - Cascading styles part two

Three methods to display a background/logo between two songs

How to remove an image assigned to a song verse

How to adjust slide text margins

How to edit the footer and header content or remove it

Display live video stream as lyrics background