Registration form input field's text have wrong colour

[perillamint]

Problem

In the current welcome screen, the register form's input field does not have a proper colour and falls back to the default (usually black) colour configuration.

In most cases, this makes it extremely hard for users to interact with the registration form.

Proposed fix

Add font colour attribute on CSS style to make it use white colour to match other texts in the screen.

[aumetra]

Closed with merge of #204