add "Tutorial" label

[mccalluc]

• Fix Label toggle with "Tutorial" #855

It's higher than I'd like, but I spent some time wrangling the CSS, and although I was able to bring the controls down, moving the "Tutorial" down with margin-top also lowered the horizontal grey line, and separated it from the tab outline.

If anyone else wants to try, feel free! If this looks too ugly, don't feel obliged to approve.

There's already a little custom CSS in styles.css for this part of the UI:

/*
The tutorial mode toggle in the navbar is positioned slightly too high.
*/
.shiny-input-container:has(#tutorial_mode) {
    margin-top: 0.15em;
    margin-bottom: -0.15em;
}