feat(Layout): update style for IsFixedTabHeader

### Is there an existing issue for this?

- [X] I have searched the existing issues

### Is your feature request related to a problem? Please describe the problem.

_No response_

### Describe the solution you'd like

```
.tabs-header {
  position: sticky;
  top: var(--bb-layout-header-height);
  z-index: 5;
}
```

### Additional context

_No response_