Blank in supervised classification

I’m usint SNAP software but I have met some problems relative to the Supervised Classification.

In particular, I’m working with Sentinel 2 data following these steps:

1- Resampling (output resolution 10)

2- Subset

3- Reprojection (WSG84)

Then, I create a new vector data container using vector polygons function but, when I open them, the style_css column results blank.

Moreover when I run the classification (MLC and/or MDC) the whole output image (Labeled classed) results black and in in frequency column of the Colour Manipolation panel I find a question mark.

Can anyone help me?

just to go sure: You first create the vector data container and then digitize the training areas?

Can you select them as inputs in the classification module?

Thank you for your prompt reply.
Yes, first I create the vector data container and then I add the vector polygons.
To reply to the second question I show you the classification screen:

can you please show the VectorData tab and what it contains? You might need to make the column larger to see the full content.

The vector data tab, contains all the selected polygons but the column “style_css” is empty.
I show you my screen:

the style_css is not important for the classification.
Are there polygons in the water geometry as well?

Yes, I have created water polygons:

hm, the only thing that I can think of then is the input bands. Are there also other ones besides B1-B12 in the list of source bands for the classification? Maybe you should try to select only the few bands which contain image information.

Dear Dr. Braun, thank you for your helpful assistance. Following your suggestion I have solved my problem (selecting only few bands…)