You probably know it, GUI modding in Stellaris is quite hard and annoying. But having a good looking event is really nice. So I created a template you can freely use and change!
Warning: while using this template is imho easier than learning gui modding and trying stuff out, it still require a basic knowledge of events and some efforts (I won't hold your hand as for the configuration above: you're gonna have to look at the template to understand).
On another note: you are welcome to modify the template to suit your needs (please credit :P). Just make sure to change the name of all of the elements you change so that you don't affect another mod using the default template.

Take a look of the dmm_template.0 event and use it as base (if you didn't download the mod, you can find it on github[github.com])
First thing to notice:
diplomatic = yes
custom_gui = "dmm_template_window"
Then come all of the options. They can be separated in 3:

• The submenus. Use them to open another page of the settings menu. One of them should be disabled (because you are currently in it), the other will fire similar events (same gui, different options).
  
• The settings. They are divided in left and right settings. On each side, there is a text and then either a checkbox or a button.
  
• The close option. default_hide_option = yes makes it selected when pressing escape.

The submenus should be pretty straightforward, just keep in mind to increment the number in custom_gui = "dmm_template_submenu_0" for each of them (start at 0, up to f in hexadecimal).
The close option should also be straightforward. You can also make it fire the DMM event if you want to (country event dmm_events.0).

The settings:
As previously stated, there is a left and a right part. You basically order your options as: left text, left button/checkbox, right text, right button/checkbox/dummy (more on that right after).
To mark a new line, you have to have a right button/checkbox/dummy. That gui generates the new line.
If you don't want a button or a checkbox, use a dummy (custom_gui = "dmm_template_right_dummy") with no text.
As you can probably tell, the checkbox can either be checked or unchecked. You probably want to have 2 options (one with each), mutually exclusive that switch between each other.

What isn't in the template (for more lisibility) is that each setting (except the close) should refire the same event.