Bar shape: Gradient band
The bar is a band in the theme's colours with white words, and the current page sits in a white pill. Scroll down and the bar tightens up (Shrink when the page scrolls).
Try the others: Pill · Segmented · Underline glide · Dock · Neon · Tabs · Tiles · Bubbles · Brutalist · Gradient band
Set it in Content > Menus > (your navbar menu) > Behaviour > Bar shape, or for one page with [navbar bar="gradient" /].