After pushing a dev instance of drupal to a server, the admin CSS broke.

Browser Console showed *.css files that were obviously auto-generated, but no amount of browser cache clearing, CHMOD, or D8 cache clearing resolved.

Here's an excerpt from the D8 forums - with the actions that were taken noted with ***

The method that has worked for me in past is below:
There may be an unneccessary step of two , but I prefer safe over sorry.

include v.s. require

• include and require only differ in that
  • require -  script will HALT if the file specified is not found
  • include -  script will CONTINUE if the file specified is not found

include

include 'include/init.inc.php';

• include will include the file - even if already included - as an overwrite.
• Previous variable declarations and functions will be replaced.

include_once

include_once 'include/init.inc.php';

• include_once will ONLY include the file if NOT already included.
• if file already included, this statement is basically ignored

require

require 'include/init.inc.php';

• Require will include the file - even if already included - as an overwrite.
• Previous variable declarations and functions will be replaced.

Define Constant

define('STATIC_CONSTANT', true);

Variable Declaration/Instantiation

$dog = 'pitbul';

$file = $tmpFile;

Based off a YouTube video where setup and config is covered; made personal notes and screen captures; and trapped errors, troubleshooting and resolutions for any problems encountered.