Instead of having dotted vertical lines underneath each {
:
It used to to have solid lines:
I know you can turn these lines off and change their color. (Found these answers while searching.) But what happened to the line style?
You can disable the lines with the option Show guides for declaration level constructs under Text Editor > C# > Advanced > Block Structure Guides.
Since Visual Studio 2017 Update 2, the soft line has been replaced by the dotted one. As far as I can see there is no option to change the dotted line back to the softer one. You can suggest this feature using Connect.