I think you are facing this problem just because of your default styling inside your style.css like:

* {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

In Tailwind v4 you need to use this default styling inside @layer base{ }. Put all the default styles inside the Tailwind base layer.

@layer base {
  * {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    scroll-behavior: smooth;
  }
}