title: How to convert height to WKWebView's coordinate
body: <p>I changed WKWebView's contentInset so i can add a headerView.but web can't be clicked within insets.<a href="https://stackoverflow.com/a/29361854/7238980">smileEvday</a> adviced me to add a empty div in HTML string, at the beginning of the body.if contentInset.top is equal to 100,height of the empty div should be 100px when using UIWebView.But I failed to calculate the height of the div when using WKWebView.if contentInset.top is equal to 100, how to calculate the height of the empty div?</p>