1.第一种方式：在WebView的代理方法webViewDidFinishLoad中：
字体大小： [webView stringByEvaluatingJavaScriptFromString:@"document.getElementsByTagName(‘body‘)[0].style.webkitTextSizeAdjust= ‘12%‘"];
字体颜色：[webView stringByEvaluatingJavaScriptFromString:@"document.getElementsByTagName(‘body‘)[0].style.webkitTextFillColor= ‘green‘"];
背景颜色：[webView stringByEvaluatingJavaScriptFromString:@"document.getElementsByTagName(‘body‘)[0].style.background=‘#F6F7F3‘"];
2.第一种方式：在下面可以通过改变margin大小来改变webview文字距离边距大小，13代表字体大小，self.strBookTips是要被操作的字符串。
NSString *BookStr = [NSString stringWithFormat:@"<html> "
"<head> "
"<style type="text/css"> "
"body {margin:10;font-size: %d;} "
"</style> "
"</head> "
"<body>%@</body> "
"</html>",13,self.strBookTips];
[self.webView loadHTMLString:BookStr baseURL:nil];
3.第三种方式，这种缺少了改变背景颜色
NSString * formatString = @"<span style="font-size:13px;color:#7E7C8A">%@</span>";
NSString * htmlString = [NSString stringWithFormat:formatString,self.strBookTips];
[self.webView loadHTMLString:BookStr baseURL:nil];