HTML development needs to be targeted to the client’s mobile device version. If a client is using iPad2, all HTML development needs to be conducted and verified on an iPad2 to ensure backward compatibility.
To make rounded corners on a container for older browsers, images of (usually) four corners would have to be created. The use of CSS3 in assets, allows the browser to take care of it and there is no need to load images into memory etc.
NOTE: HTML files are treated as local files file://...(Instead of http://...) and there are other rules e.g. cookies don’t work, so HTML5 localStorage has to be used.
Always test your asset on a device. Just because it works in Safari on the desktop may not imply it works on the device.