Re-enable custom height for flatpage content field in admin

[Baptiste Mispelon]

The admin's forms.css file contains this rule [1]:

.flatpages-flatpage #id_content {
    height: 40.2em;
}

The purpose of this rule (I'm guessing) is to make the FlatPage.content field taller on the add/change form, because this field typically contains a lot of text. This appears to be basically as old as the admin itself, and was added in dd5320d1d56ca7603747dd68871e72eee99d9e67 (where it started as body.core-flatfile #id_content { height: 400px; }).

However this rule doesn't currently do anything, because the .flatpages-flatpage selector doesn't match anything.

This appears to be a regression that was introduced in release 1.6 with commit bb145e2c47d71b7f68280c00ced727442d2effa2 wich effectively changed the body class from flatpages-flatpage to app-flatpages model-flatpage.

[1] ​https://github.com/django/django/blob/1167cd1d639c3fee69dbdef351d31e8a17d1fedf/django/contrib/admin/static/admin/css/forms.css#L360-L362

[Antoliny]

Thank you Baptiste!
As you mentioned, it seems that the #id_content was intended to make the Content field larger on the FlatPage model Change/Add form.
However, I wasn’t able to find any part of the admin where this CSS is actually being applied.
And thank you for adding detailed information to the ticket, it really helped me understand and verify the issue!

[Khanh Vy Nguyen]

I will take this task as my first contribution to the django project.

[Baptiste Mispelon]

Replying to Khanh Vy Nguyen:

I will take this task as my first contribution to the django project.

Hi 👋🏻,
Thank you for your interest, but this ticket already has a patch attached (see the "Has patch" field).

[Antoliny]

Replying to Baptiste Mispelon:

Hi 👋🏻,
Thank you for your interest, but this ticket already has a patch attached (see the "Has patch" field).

Hello Baptiste, do you happen to know where this PR is? I couldn’t find it anywhere...

[Baptiste Mispelon]

Replying to Antoliny:

Hello Baptiste, do you happen to know where this PR is? I couldn’t find it anywhere...

It's not a PR, it's attached as a patch to this ticket (see "Attachments" at the top)

[Jacob Walls]

Thanks, a PR would be helpful at this point.

[Baptiste Mispelon]

Replying to Jacob Walls:

Thanks, a PR would be helpful at this point.

Sure thing, here you go: ​https://github.com/django/django/pull/19958

[Jacob Walls]

Tangent: seems a bit odd to be doing this with CSS instead of in flatpages/admin.py via the rows attribute on the <textarea>, but happy to merge this (well spotted!)

[Jacob Walls <jacobtylerwalls@…>]

In 2b62951f:

Fixed #36659 -- Fixed flatpage content selector in admin forms.css.

Regression in bb145e2c47d71b7f68280c00ced727442d2effa2.

[Jacob Walls <jacobtylerwalls@…>]

In 094797a:

[6.0.x] Fixed #36659 -- Fixed flatpage content selector in admin forms.css.

Regression in bb145e2c47d71b7f68280c00ced727442d2effa2.

Backport of 2b62951fecf0024ce9ce0ce9f5be512c10747c0d from main.