I realize I'm cutting corners here, hoping to avoid having to become an Illustrator expert to do something so simple. However, here's my experience:
1. Open my original SVG into Illustrator. It contains a <rect> element and five <line> elements, all of which have a style attribute that includes stroke-width:3 (I've attached the file). So as I understand it, my goal is to convert those strokes to fills.
2. In Illustrator CC, I choose Select > All.
3. Then I select Object > Expand.
4. A dialog appears, with three choices: Object (grayed), Fill, or Stroke.
5. It's unclear to me whether this dialog is prompting me for the source (i.e., What do you want to expand?) or target (i.e., What do you want to expand *to*?), so I try both.
If I choose "Fill", then save the file to SVG, the result includes <line> elements with fill="none" and stroke-width="3", which presumably is not the desired result.
If I choose "Stroke", then save the file to SVG, the result is a file where all objects have been converted to <rectangle> elements.
If I choose both "Fill" and "Stroke", then save the file to SVG, the result is the same as if I had just selected "Stroke".
In all cases, when I save as SVG I have lots of SVG Options to choose from. I'm accepting the default settings. In all cases, if I import the new SVG file into the icomoon app, it shows up as a solid black square.
What am I missing?