Add placeholder to avoid empty input fields from jumping

[frederike-ramin]

Short Description

• When you inputted a value into the first field of the unlock_code (and IdNr) field, the field was not aligned with the others anymore.
• This is due to the fact that Safari has a bug that makes the baseline alignment not work as intended on empty input fields in a flexbox with baseline alignment: iOS Safari: align-items calculates baseline as bottom of input element philipwalton/flexbugs#270

Changes

• Added an empty placeholder, because then the field is not technically empty and the fields are correctly aligned (solution from the above post)

Feedback

• Do you see any problems with this?

[nfelger]

Excellent find! The line you added desperately needs a comment though - no one will understand why we add a space as the placeholder.