Today Elevenfour released the first Beta Version of Dark Core for WoltLab Suite 5.4. The new version comes with an improved color scheme for the header area. I've also managed to remove SCSS, that was no longer neccessary - that's why the style no longer uses parts of WoltLab's SCSS in the additional SCSS.
Please note that this style does exclude the final version of WoltLab Suite 5.4.0. A final version of this style will be available in the future. It is not possible to upgrade the style from version 5.2.x or 5.3.x - that is for the beta and the final version as well. The reason for this is that the style update system of WoltLab Suite does not allow for color changes.
Screenshot of the new Dark Core style