Fix SigningBox shadowed by background of offramp summary dialog

[ebma]

Context

The SigningBox is currently shadowed by the darker background of the offramp summary. This removes the focus from the signing process. Instead, both dialogs should be visible shining in a bright shade of white.

TODO

Make sure the SigningBox is not shadowed but appears on the same a higher level than other dialogs. It should be prominently displayed as the current call to action. Ideally the signing box stays in the bottom left corner.

[prayagd]

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