I have set Customizer -> Button to both Flat and Square, yet in Cornerstone when I use the new Button element all Buttons appears as Rounded and 3D…See attached.
Note that when I use the Classic Button element it works as expected, taking the settings from Customizer.
Somewhere the Customizer code seems to be overwritten and is not consistent with the legacy/classic button. I want the flat/square ones, but cannot get the Element to take that style.
You are correct, the setting that you see in X > Theme Options > Buttons work only for the Classic Button elements. The new V2 button element has its own styling. For more information please read the article below:
Now, there is a new feature called the Template Manager. The way it works is that you add a Button element and using the options given to you by that element you can make the button flat. Then you can make a template of that button and set that template to be the default view of the button element.
After that, whenever you add a new button element you will have that flat style. Please check the article below for more information about the case:
The cool thing about the method above is that you can do this for every none classic, V2 elements.
Additionally, please make sure that you will enable the Advanced Mode if you want to have a complete control over the options of the elements. Read this changelog to know more about the advanced and simple mode.