How you can have styles that only target the Yahoo! Mail Android app, using a simple workaround.
Yahoo! Mail HTML codes
You can target the Yahoo! Mail iOS app by using the @media yahoo and adding a max-width to the media query.
You can target Yahoo! Mail by using the @media yahoo media query and adding your styles.
Gmail and Yahoo! Mail add a spacing between images. This issue first showed up when viewing emails in Firefox and later spread across other modern browsers including IE, Chrome, Opera, and Safari.