Nothing wrong with your epub. The issue is that ReadEra is not the best app to read an epub; in fact, it doesn't honor the css styles inside an style sheet. You have to define your own styles "on the fly" in the very app. There, you must define the font you want, its size, the alignment of paragraphs, their line-height, the margins of the page. And that's all; you can't define anything more.
You'll have better by choosing any other app to read your epub: PocketBoot, Aldiko Next, Lithium, Reasily, Gitden Reader (if you can find it), Bluefire, OverDrive. And if your epub doesn't have some very advanced epub3 properties, you also will be able to read your ebook in BookFusion and Colibrio Reader. Even Infinity Reader will honor so simple css stylesheet like yours. Of course, you have set "Times New Roman" or Times as fonts; if your smartphone doesn't have them, the ereader app won't be able to show them
