css – How to change the color of the SharePoint Online navigation header?

Here is some basic information, I will also include a summary:

I have a problem with the SharePoint Navheader color, which seems to have changed in the last two weeks as a result of an update of SharePoint / Office 365. The release notes mention a new feature with "a new look of the Office 365 navigation bar in SharePoint Online ", see the specific update notification in the screen capture.

Update Notification 14/02/2019

By clicking on the "additional information" link at the bottom of this notification, you will be directed to a blog post that says: "The work you have done for OneDrive and SharePoint will remain".

enter the description of the image here

But it turned out that this was not the case: the branding of the company had disappeared, replaced by the personal theme O365 NavHeader of each user. Here is a screen shot that shows what my mine looked like:

SharePoint NavHeader with an incorrect mark

The light blue color is NavHeader. Assumed to have, but not. The screen capture includes the highlighted item and the Style Viewer. I should mention that the whole class looks different from what it was.

SharePoint uses classic pages, but modern document libraries. Another company was outsourced to tag pages and used custom CSS stylesheets for traditional pages, while modern document libraries were associated with theme packs installed by PowerShell. Now these two types of page have their NavHeader displaying the theme that the user viewing the pages has set for their personal O365. Here's a screenshot of the CSS that controlled the displayed color:

CSS Branding

This part has been modified internally during a recent brand change and has worked perfectly in the last 5 months, but we suspect this recent update to make changes that have somehow broken the brand image .

TL; DR / Summary: A recent update (around 14/02/2019) broke our SharePoint brand image. Is there a simple way to restore brand colors for NavHeader in SharePoint Online? Or does anyone know what could be the cause of the loss of our brand image, despite the release notes stating that this should not affect the brand image? See screenshots for more information.

The hope is that we could handle this with the available resources (limited SharePoint / CSS knowledge). Do ask if you need more information. I have tried searching for all the latest issues in the last few weeks in case someone reportedly reported similar issues as it is a very recent update.