If this commit now it is possible to define a custom theme directly
using Nix, like this:
```nix
{
programs.rofi.theme = {
"*" = {
background-color = "#000000";
border-color = "FFFFFF";
width = 512;
};
listview = {
cycle = true;
};
};
}
```
And this will be converted to the proper rasi format to be used in
rofi.
