Accuracy of HTML and CSS.
Appropriateness of the SSL certificate for respective browsers.
End-user forms, fields, and webpages with and without JavaScript.
Accuracy of DOCTYPE for every webpage.
Accuracy of the layout across various screen resolutions.
Font attributes like format, size, and color should be consistent across various platforms.
Content alignment of applications across various screens.
Working of images, audio, video, and other multimedia technologies.
Consistency of navigation within the application.