The system status report has been made into a CSS component in Drupal 8.
As a result there are a couple of new classes.
Drupal 7
.system-status-report .status-icon
Drupal 8
.system-status-report__status-icon
Drupal 7
.status-icon status-icon--{{ requirement.severity_status }}
Drupal 8
.system-status-report__status-icon--{{ requirement.severity_status }}
Drupal 7
.system-status-report .status-icon--error
Drupal 8
.system-status-report__status-icon--error
Drupal 7
.system-status-report .status-icon--warning
Drupal 8
.system-status-report__status-icon--warning
Drupal 7
.system-status-report .status-title
Drupal 8
.system-status-report__status-title
A new class has also been created to reference each entry of the system status report table:
Drupal 7
<tr>
Drupal 8
<tr class="system-status-report__entry">