Hi Fabio,
Are you sure you are defining the CSS on the webscreen CSS editor?
If yes and if its still not working - one possibility is that the CSS is being overridden by OutSystems.
You can in that case try:
[id$="MainContent"] {
word-wrap: break-word !important;
}
or
div.content-middle {
word-wrap: break-word !important;
}