Layout builder's "Add Block" sidebar menu UX improvements

This looks much better and its a very simple fix. I've been wanting the collapsed fieldsets for a while and the colored CTA button is a great addition.

I love this!!

Also tagging, as this came up in recent UX testing the Acquia Customer Experience team did (still working out a way to help get these results public). These changes would go a long way towards addressing problems with e.g. noticing there's an "Add new block content" option to begin with, and the overwhelmingness of the list of blocks, for example.

And since this is a primary interaction that's confusing people, escalating to "major" and a "task."

Cross linking with another issue as this introduces more usage of the word "inline"

So, it passes the tests for 8.8, but has a few failures for 8.7

Does that mean backporting any test changes from 8.8 to 8.7?

Let's have the most recent patch be for 8.8 since that has to happen first.

1. +++ b/core/modules/layout_builder/css/layout-builder.css
   @@ -133,21 +133,28 @@
    }
    
   +
    #drupal-off-canvas .inline-block-list {
   

   Nit: no need for an extra line here

2. +++ b/core/modules/layout_builder/src/Controller/ChooseBlockController.php
   @@ -119,16 +119,23 @@ public function build(SectionStorageInterface $section_storage, $delta, $region)
   +      '#attributes' => ['class' => ['existing-block-create-title']]
   

   I think this needs to be BEM-ified

3. +++ b/core/modules/layout_builder/tests/src/FunctionalJavascript/LayoutBuilderUiTest.php
   index 06b32a0eb4..b1bed1e7ed 100644
   --- a/core/themes/stable/css/layout_builder/layout-builder.css
   
   --- a/core/themes/stable/css/layout_builder/layout-builder.css
   +++ b/core/themes/stable/css/layout_builder/layout-builder.css
   

   Can't change the stable CSS, afaik

Removed the empty line in #14.1, and removed the CSS class in 14.2 as I didn't see it being used anywhere.

As for 14.3, I updated the CSS to add a new selector and added that to Stable so that no existing Stable CSS is being changed.

Looks good, just two small nits

1. +++ b/core/modules/layout_builder/src/Controller/ChooseBlockController.php
   @@ -119,16 +119,22 @@ public function build(SectionStorageInterface $section_storage, $delta, $region)
   -        $build['add_block']['#attributes']['class'][] = 'inline-block-create-button';
   +        $build['add_block']['#attributes']['class'][] = 'inline-block-create-button inline-block-create-button--large';
   

   This original line should be left as-is, and copied to add the second class (each as its own array entry)

2. +++ b/core/modules/layout_builder/src/Controller/ChooseBlockController.php
   @@ -119,16 +119,22 @@ public function build(SectionStorageInterface $section_storage, $delta, $region)
   +      '#plain_text' => $this->t('Add existing block')
   

   Missing trailing comma

Fixed nits as described in #16.

Pushing back on this for now, I believe there's been more design work here and it needs to be represented here.

One thing our editors have been confused about is why there's seemingly two separate lists of blocks.

There's the main list you see when you click "Add block", and then there's this secondary list that's only revealed when you click "Create custom block". Why is this separation needed? Yes, behind the scenes, these "custom" blocks are distinct because they represent the creation of BlockContent entities, but to a site builder, all blocks are layout building components.

It seems that when content blocks were first added to layout builder, they were shuffled in with the main list of blocks, but it was changed in #2968500: Change inline blocks workflow in Layout Builder to match mocks to separate them.

I agree that the UX improvements proposed in this issue are indeed improvements, but I propose that this issue be closed and instead effort be focused in improving the overall block selection UX in #3073648: The list of available blocks in Layout Builder is overwhelming to users.

I agree that custom blocks need to be moved back to the main blocks list. I have read through the issue that caused this change and still do not see a good reason for said change, but it seems like really, really bad UX. It is confusing to users and unnecessary, as to them, there is no meaningful difference between custom blocks and other types. Also, if you click on "Create custom block" and you want to then go back to the main block list, you can't. The only option is to close the panel and start over. Plus, the search box does not work for custom block types in the current configuration. Please move it back, or provide a simple means for us to do so.