How to set a sticky header
The following steps are available for a 1.9 theme version or above
WP Admin > Appearance > Headers/Footers and edit your header.
Select the fixed position for the header.
- Check the "bottom padding" option and save the settings.
Note for the 1.8.7 theme users
The sticky header option is located in WP Admin > Appearance > Customize > Header design and check the "Sticky the menu on scroll".