Hi Simin, can I suggest that you provide more detail or at least a screenshot or example of what isn't working for you and/or what you're actually trying to achieve? There are so many variables for header design and layout that it is highly unlikely that anyone can offer you a clear answer at this time based on the available info.
For what it's worth, I can have a logo (left-aligned) on my survey with a header containing a rich text string (again, left-aligned) and all of this would align perfectly with my questions. If I started adding in graphics, HTML coding etc into my header, then that adds complexity that might cause my header to be out of alignment with my logo and/or questions.
Cheers,
Cameron

Hi CamM,
Many thanks for your reply, I want to get rid of the gap showed by the arrow:

Try this CSS:
.Skin #Header { text-align:left; }