Replace strong tag with CSS in template_preprocess_authorize_report and remove id..

I agree, title changed and lets do that here. The class name may need to be BEMized. @see component in https://drupal.org/node/1887918

Maybe move authorize-results to a class and rename .failure to .authorize-results__failure?

This patch should be possible on it's own. That other issue is a conversion from theme_ function to twig template so other than maybe a merge conflict this should be still good to go. Conversion issues should be straight conversions as much as possible, no new features added.

#4 Looks fairly good. Just make the patch against 8.x branch.

+++ b/core/modules/system/css/system.maintenance.css
@@ -43,3 +43,10 @@
+.authorize-results__failure {

the class is called .failure and it would be inside .authorize-results and not bemized yet. Though you could "bemize" them I think that is scope for a different issue.

Sorry for the late response @mrjmd, but thanks for the patch nevertheless.

@mrjmd thanks for the new patch, here's a review:

1. +++ b/core/includes/theme.maintenance.inc
   @@ -155,7 +155,7 @@ function theme_authorize_report($variables) {
   -    $output .= '<div id="authorize-results">';
   +    $variables['attributes']['class'] = 'authorize-results';
   
   @@ -176,7 +176,6 @@ function theme_authorize_report($variables) {
   -    $output .= '</div>';
   

   This is the only change that may be a bit premature though I like the idea very much. The problem is you added a class that that never gets used(may get used in the twig template... I don't know). Two options here, just remove the div all together, or the more pragmatic approach just change the id to class in the string. I'd favour the latter.

2. +++ b/core/modules/system/css/system.maintenance.css
   @@ -43,3 +43,10 @@
   + * Theme maintenance styles
   ...
   +.failure {
   +  font-weight: bold;
   

   This should be prefixed with .authorize-results class just like:
   .update-results .failure further up the page.
   Or for bonus points do the bem naming like you did earlier and not worry about naming collisions. I'm not sure when/where those bem naming are to go in or which issues they are from but worth a shot. But to be on the safe side you could just copy the pattern before you.

3. +++ b/core/modules/system/css/system.maintenance.css
   @@ -43,3 +43,10 @@
   +}
   \ No newline at end of file
   

   This needs a newline.

+++ b/core/includes/theme.maintenance.inc
@@ -198,7 +198,7 @@ function theme_authorize_message($variables) {
     $item = array('data' => $message, 'class' => array('success'));

Should we do success here too? to make them consistent in naming pattern? Otherwise this is RTBC from me.

Awesome, this looks great to me. I double checked and there are no css or js in core using the ID or class for these theme so we should be good there.

Not exactly sure how to get to the page to see this though for manual testing...
One part of the puzzle is turning on allow_authorize_operations = TRUE in settings.php from the authorize.php docblock.

Thank you @alexpott :)