Fix working icon placement on password save

Before, the icon appeared below the text input for the password. Now, it
appears inside the text input, to the right end.

The CSS was adjusted based on other icons shown in that position for
other text inputs in the Share tab view, like the information icon or
the clipboard icon.

Fixes #4135

Signed-off-by: Daniel Calviño Sánchez <danxuliu@gmail.com>