字体大小
[webView stringByEvaluatingJavaScriptFromString:@"document.getElementsByTagName('body')[0].style.webkitTextSizeAdjust= '200%'"];
字体颜色
[webView stringByEvaluatingJavaScriptFromString:@"document.getElementsByTagName('body')[0].style.webkitTextFillColor= 'gray'"];
页面背景色
[webView stringByEvaluatingJavaScriptFromString:@"document.getElementsByTagName('body')[0].style.background='black'"];