How to remove line break character \n in regular expressions?

Question

Regular Expressions

There is a function that replaces the content in a tag with other content.
But if there is a line break character \n in the content, then the function stops working.

public static string zamLang (string str, string id) {
  string returnString = Regex.Replace(str, "(?<=<size>).*?(?=</size>)", Lang.lang(id));  
  return returnString;
}

For example if
string str = "Первая строка \n Вторая строка"

Answer 1

RegexOptions.Singleline