Problems with designing a square layout

Hallo.

I would like to design a new special square keyboard layout in Onboard.

It is called the EINERST-Layout, which is a layout optimized for one-finger or stylus use, especially for the German language.

The basic idea is to gain speed in one-finger or stylus typing by reducing the distances between frequently used letters and keys.

The center of the layout looks like this:

d e i n f
, SPACE .
l r s t h

An image of the complete layout (designed with Comfort Software On-Screen Keyboard): https://postimg.cc/Mn5YYwt6

There some basic design principles:
1. In order to have small distances in one-finger or stylus typing, the more frequent a letter is, the more centrally it is positioned in the layout.
2. The shortened space bar is positioned in the center, because Space is typed often, even in languages with long words like German, and the use of space is quite uncorrelated with the use of any other key. This ensures that the finger or stylus is often placed in the center of the layout.
3. Comma and full-stop are positioned next to space, because the space key follows the comma and full-stop key almost automatically.
4. letters of frequent n-grams (like "qu", "in", "an" ...) are positioned near to each other.
5. The use of an almost square layout reduces distances overall.

This works quite well for me in the German language, and I think it could also be useful in other languages related to German like English (hence the th-combination).

I tried to design that layout in Onboard by copying the full layout of Onboard to a new layout and opening the resulting alpha-svg file in Inkscape but when I transform the layout to a square or when I adjust the heights and widths of the keys and save the new svg file, I can open the new layout but the file is transparent, no keys are shown. But, when I type "blind" on the transparent Onboard keyboard, keys are pressed.

I would like to know what is my error, what am I doing wrong.

Thanks in advance,

Alex