I'm having a super annoying problem with CKEditor.
When I first load it, it appears like this:

then, when I click inside to type, it goes like this:

ok, everything just fine, but look what happens with the content when I type something:

I don't have any Arial 12 labeling, so when I get this HTML and process it, I'll never know it should be Arial 12.
Now, if I manually change it, then it works, but when I click outside the CKEditor window and then back inside again, it returns to the initial state, with no tags, look:

I've tried every solution on google, like adding
font-family: sans-serif, Arial, Verdana, "Trebuchet MS" !important;
font-size: 12px !important; in content.css,
or adding
config.font_defaultLabel = 'Arial';
config.fontSize_defaultLabel = '12px';
in config.js, etc.
Could someone help me, please?