It's a tricky subject.
Your game already suits mobile very well I think but could maybe be enhanced with a bespoke font.
Maybe use an 8 bit font. To try it out just select menu/import then choose a TTF file.
I think your game would suit a "pen" colour of #fff, and keep the other colour settings as they are.
For 8 bit fonts as above, maybe choose a paragraph spacing multiplier of 1.
Check out the fonts here....
https://damieng.com/typography/zx-origins/
There are lots of things to try. You can also use multiple themes and allow the player to select at runtime via one of the ask commands and set theme.
Check out THE BEAST 30TH ANNIVERSARY for an example of theme choices at the beginning of the game.