Compact version of Linux to use in a virtual machine with Pale Moon

I’m looking for a compact version of Linux to use in a virtual machine. I must be able to use the Pale Moon web browser in it. (Don’t waste your time singing the praises of other browsers.)

What do I mean by ‘compact’? Probably 300MB to 500MB download size. 700MB download size at the outside.

What VM software am I going to be using? Probably VirtualBox. I’m aware from previous experience that some Linux systems run badly in VirtualBox. The uncontrollable mouse pointer is a particularly common problem.

What guest system am I going to be using? At the moment an older Mac system (don’t waste your time telling me to update it); later possibly Windows (not sure what version).

Have you tried antix? Very lightweight and runs like a dream. I’m using mxlinux(same developers) as my main os. Its more medium weight but very well packaged.