MDL-43284 only fixed some of the issues. There are sill some issues on those pages which mean that clean is not good enough to be the default theme in 2.7. They need to be fixed. Please see https://tracker.moodle.org/browse/MDL-43284?focusedCommentId=279717&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-279717
This can all be fixed with CSS.