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Step-by-step guide to create a “Seven” sub-theme for Drupal 8

Step-by-step guide to create a “Seven” sub-theme for Drupal 8

Working in Drupal means always being open to learn new things. Nothing stays the same for long and there’s so much to pick up that you may not have before encountered.

Today, that came in the form of an administration theme that went awry. (Enough talk: give me the tutorial.)

I’ve been trying to sub-class “Seven,” which is Drupal 8’s default admin theme, and which is, itself, a sub-theme of “Classy.” This had not been going well for me. While I was able to create and enable the theme,  it certainly didn’t quite work the way it was supposed to.

For example, when I followed (to the letter) the example by Si Hobbs  on the Lil Engine “Subtheme your admin theme” post, I noticed that the wrong blocks were being placed at the top of the block layout.

Seven sub-theme block vomitted

Checking admin/structure/block showed that not only are blocks placed in the wrong spot, but there are also blocks missing.

Seven sub-theme blocks missing

The funniest thing is how hard it was to find good examples of people trying to sub-theme “Seven.”

Then, while I’m working on this post, I search “drupal 8 place block on theme install” and get this as the top result:
How to Assign Blocks to Particular Regions on Theme

I’m trying to do what Vadim is doing: create a sub-theme of Seven and have the blocks placed somewhere on install.

But there is not one, no, not one single example of someone walking through in any detail the steps completely. So why not show what I did and what worked and didn’t so that if anyone else ever finds this post they will be able to do exactly what I did and get the same result?


Despite the issues I encountered, I am extremely grateful for the work that was done and shared by Si Hobbs for Lil Engine and the post and subsequent conversation between vadim.jin and Jeff Burnz. They laid the necessary groundwork to get this working for me. The last mile divide was bridged with the help of my coworkers, nixter and Kikki Beltz.

How to Sub-theme Drupal 8’s Seven Administrative Theme


You have some familiarity with Drupal 8, though not necessarily that much. Perhaps you are a site builder or a site developer from Drupal 7, who is trying to get familiar with Drupal 8. In any case, you know how to

  • install a Drupal 8 site
  • access the Drupal 8 file system
  • use the Drupal 8 admin GUI

Step 0 – Have a Drupal 8 site

Start with an installed Drupal 8 site.
(I know this assumes a lot, but if you use Acquia Dev Desktop, it gets easier than going the MAMP route.)

I used my local site on Acquia Dev Desktop.

Step 1 – Exporting configuration files

Export configurations by going here:


Configuration export
Configuration export

Run the export

Step 2 – Change the necessary exported files

Pull the files mentioned here:
Drupal 8 Admin Primary Tabs Completely Disappeared


Change the filenames like so:

Then, go into each of the YAML files, replacing any mention of “seven” with “mytheme” and removing UUID and config hash:

Config YAML files diff

Make sure to do that to each of the four YAML files.

Step 3 – Create the file structure for the theme

This directory goes inside the site root folder. In Acquia Dev Desktop, it’s where you end up when clicking the link next to “Local code”. As you can see, my site is creatively called “drupal–8.5.0,” which was the default name given by Acquia Dev Desktop.


You will need to create the “custom” folder first.

Sub-theme file structure
Sub-theme file structure

In the theme folders, make a set of files as below (linked), which is basically my crib of the Lil Engine’s code.
• mytheme.libraries.yml
• css/admin-styles.css

Step 4 – Add the YAML files

Create the following in your “mytheme” directory:
add those 4 YAML files to the directory, so that the files should look like so

Sub-theme file structure with with YAML files
Sub-theme file structure with with YAML files

Step 5 (optional) – Make a new screenshot

I just copied the screenshot.png from Seven and added a name in front of it, using an image editor.

Then I save it as screenshot.png

Plus, I added the file path to the file.
“screenshot: screenshot.png”

(Note: the “screenshot” key is  necessary, but the file name can be whatever you want. I also changed it to logo.png in another iteration, to keep it distinct from Seven–just for my own sanity.)

This step of adding a customized screenshot is also described briefly in Lil Engine’s post.


If you need to make changes to the theme after setting it as the admin theme (especially if they relate the YAML files).

  1. Set “Seven” as the Administration
  2. Uninstall “My Theme”
  3. Make necessary changes to the theme (like adding files to the config/install folder [or changing said files])
  4. Install “My Theme”
  5. Set “My Theme” as Administration
  6. Clear cache (of course, right?)


If you try to use this guide and run into trouble, let me know. I would love to improve it where improvement is necessary.