How to make this type of nav themes is this images or sllices
Use browser dev tools to inspect one of the links and you should be able to figure it out.
No these are not images. Probably done using buttons with a gradient background. All done in CSS. Take a look at https://www.w3schools.com/howto/howto_css_button_group.asp this should get you started and then just play around with the CSS styling. You will want to add a margin-right to the btton definition to separate the buttons.