To achieve this sort of effect:

1. You need to change your caves "Render Mode" to "Screen space - Camera".

You might have did it already as you are using particles but still to ensure you change the canvas "render mode".

2. Now Change "Order in layer" to 0 for particles system.

3. Add a component "Canvas" to the UI which you want to show up on the particles. In your case add "Canavs" to "drop_down_list_root".
4. Now check the "Overriding sorting" and change "Order in layer" to some thing higher then particle's "Order layer" like:

And that's it. I hope this will resolve the issue you have. If it does make sure to accept and up vote the answer.

To achieve this sort of effect:

1. You need to change your caves "Render Mode" to "Screen space - Camera".

You might have did it already as you are using particles but still to ensure you change the canvas "render mode".

2. Now Change "Order in layer" to 0 for particles system.

3. Add a component "Canvas" to the UI which you want to show up on the particles. In your case add "Canavs" to "drop_down_list_root".
4. Now check the "Overriding sorting" and change "Order in layer" to some thing higher then particle's "Order layer" like:

And that's it. I hope this will resolve the issue you have.