[FIND-447] Giving a backdrop of white to preview document iframe.
[FIND-447] Giving a backdrop of white to preview document iframe.

This is due to the fact that the documents are rendered in html format, without a default backdrop (hence transparent). The documents are rendered on the well container that's coloured grey, hence we see it through in the documents. Now the ifram itself is just white.

[rev:rosie.taylor]

hpe-idol/java-powerpoint-report,hpe-idol/find,hpautonomy/find,hpautonomy/find,hpe-idol/find,hpautonomy/find,hpe-idol/find,hpe-idol/find,hpautonomy/find,hpautonomy/find,hpe-idol/java-powerpoint-report,hpe-idol/find