Wrong Font and Background Color on SharePoint site

I've created a Power App with specific fonts and background color in Segue UI to match SharePoint. I've embedded it in a SharePoint page, but the background is changed from 240,240,240 to 255,255,255 (a minor difference, but definitely noticeable) and the fonts on all txt labels are a few points larger.

I do have a custom size on the app of 364 x 300 and matched that in the embedded iFrame. The setting, "Resize to fit webpage," on the embed webpart doesn't make a difference either way. My app display settings below. Does anyone know how I can get SharePoint to honor my fonts and background?