Regarding the font size, you need to target the submission view since emailed/saved forms are read-only. Depending on whether you're wanting to target specific fields, all fields, or all fields within a specific class (recommended), something like this should work.

One field:

#q22 input,
#q22 label,
#q22 div .submission-view {
  font-size: 20pt !important;
}

All fields:

input,
label,
div .submission-view {
  font-size: 20pt !important;
}

All fields with a custom class (I'd recommend going this route):

.ClassName input,
.ClassName label,
.ClassName div .submission-view {
  font-size: 20pt !important;
}

Checkboxes are trickier. I would check out this thread and see if any of those solutions will work for you.