fix(styles): Adjust heading styles

[susnux]

• Resolves: [Bug]: h3 to h6 look like text, headings generally inconsistent across apps #43393

Summary

Make headings look like real headings and not just ordinary text.
The styles are copied from the text-app where a design review was done on them.

Screenshots

before	after

Code used:

<h2>This is a h2</h2>
  <p>This is a paragraph</p>
<h3>This is a h3</h3>
  <p>This is a paragraph</p>
<h4>This is a h4</h4>
  <p>This is a paragraph</p>
<h5>This is a h5</h5>
  <p>This is a paragraph</p>
<h6>This is a h6</h6>
  <p>This is a paragraph</p>

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)

[ChristophWurst]

Looks great!

Settings are a bit inconsistent because those rendered with Vue are using NcSetttingsSection and it has font-size: 20px for .settings-section__name.

There are also a few headings that should be demoted to simple text, like here for external storage:

Not sure if we want to do this here or in a follow-up. Settings probably need a bit of a design review after this change.

[szaimen]

Not sure if we want to do this here or in a follow-up. Settings probably need a bit of a design review after this change.

I would do it in a follow-up

[szaimen]

Screenshots look great :)

[ChristophWurst]

Apps that use NcAppNavigationCaption

Before	After

[susnux]

If we agree on this changes here we should adjust nextcloud-vue styles accordingly.
Changes on the library will not conflict with older nextcloud versions but the fix it for 29 (this change here)

[susnux]

@jancborchardt do we want to use this styles or adjust them because of nextcloud/text#5515 ?

[ChristophWurst]

It's showtime

[ChristophWurst]

Let's add this to the app dev upgrade docs as "breaking" frontend change

[jancborchardt]

Looks good @susnux but maybe as a follow-up it would make sense to adjust it to the sizes in https://github.com/nextcloud/text/pull/5594/files ? Maybe from h1 → h2 though because h2 is the first visible one (h1 is always the logo).

[susnux]

But maybe as a follow-up it would make sense to adjust it to the sizes in https://github.com/nextcloud/text/pull/5594/files ?

Sizes adjusted ✅

Maybe from h1 → h2 though because h2 is the first visible one (h1 is always the logo).

Done ✅
But the latter is not always true. h1 is not the logo but for apps the app name (e.g. "Dashboard") or similar (for files it is the view (e.g. "All files").