Text Is Showing Up White in IE

I recently installed WP Rocket, which they say will help my site run faster. They have some settings for CSS minification that they instruct you to turn off, incase you notice something about your site has broken.

Well, I recently noticed that all my text: P, H1-H6, had turned white. Obviously, this seemed “broken” so I turned those CSS minification settings off. But the text stayed white! I even uninstalled the WP Rocket plugin, and that didn’t change a thing. I tried re-installing the theme fresh. Nothing.

I searched and searched and couldn’t figure out how to fix it, until I submitted a trouble ticket and the developers advised I paste this into my custom CSS area:

#maincontainer h1, body {
    color: unset !important;
}

(you can replace h1 with any header or even P to have same effect)

Anyway, this got my text back to black in Chrome, Safari, and even Firefox.

But my website viewers on IE are still seeing white text everywhere.

Please, does anyone know the CSS that is compatible with IE to solve this? Or some other workaround?