The main differences I can see are:
-color: a quick fix could be setting the color to 'primary and edit the scss ‘primary’ variable.
-width: the width of the elements on top is set to fit the content, while the one in your example is a constant value. Adding ‘width: fit-content’ and ‘display: inline-block’ should do the trick.
For the scrolling part you can check this post made by another user: Hide header on scroll
For the third question I’m not sure what you’re asking. Hopefully I can help if you can give more details.