Gin makes Navigation toolbar position fixed

After some more investigation: it should likely be fixed for Gin theme in the backend, but typically not for the frontend theme.

One way around is adjusting the margin on:

.gin--navigation-top-bar--offset {
  margin-top: calc(54px + var(--gin-spacing-s));
}

..or maybe a safer way around, set it back to sticky, but make an override for the admin pages, typically .path-admin [...] {display:fixed}

There are some explicit decisions in Gin's top-bar.css where I'm not aware why:

Problem 1: top position of the main canvas

The navigation module sets that to the height of the top bar:

  .top-bar:has(.top-bar__tools:not(:empty), .top-bar__context:not(:empty), .top-bar__actions:not(:empty)) ~ .dialog-off-canvas-main-canvas {
    margin-block-start: var(--admin-toolbar-top-bar-height);
  }
}

Gin sets the margin-block-start: 0 which is because Gin also sets the height of the top bar to auto, so it doesn't know the height.

Problem 2: top bar opacity

Gin sets opacity and a blur on the top bar.

We need to find out why that has been don that way before we make any changes. @saschaeggi could you please throw some light on this?

This is awesome, thanks @saschaeggi for fixing this.

Note that the navigation module does not set sticky so we kept the fixed state

Note: The opacity and blur, that I described a "Problem 2" in #3 is by design.