[TYPO3-templavoila] Flexible Content Element: BE user changes BG image

[Daniela Waranie]

Hi Newsgroup,

i defined a unmapped field in TemplaViolá (when creating a flexible content 
element).
This field  for selecting a background image in backend by a writer.

How do i force this image setting to the style attribute of a <div>-tag?
The target <div>-tag is the root for this flexible content element.

How does the TypoScript look like?

Best regards
Daniela