Delete:
activity_main.xml
Possible overdraw: Root element paints background '#0099cc' with a theme that also paints a background (inferred theme is '@style/AppTheme')

strings.xml
The resource 'R.string.dummy_button' appears to be unused
The resource 'R.string.dummy_content' appears to be unused

Declaration redundancy
Declaration access can be weaker:
main
Can be private

Verbose or redundant code constructs
Redundant type cast:
main
Casting 'findViewById(R.id.webView)' to 'WebView' is redundant