With this free module for PrestaShop 9.x, 8.x, 1.7.x and 1.6.x you can create "sticky" header in your shop. Addon works with default-bootsrrap and classic templates and with all themes with similar structure. Sticky header is activated once you will scroll page down. Fixed header will be sticked to the top edge of your shop.
As you already know this module creates "sticky" header in default template in PrestaShop 1.6.x and in classic theme in PrestaShop 1.7.x, 8.x, 9.x. Module is dedicated for default themes and each theme that has similarstructure of heading section. Module is free and you can download it without any kind of register proces etc.