Maybe but that’s not the purpose of these theme as they only adapt on grey colours the new default UI. The new UI was on Github as a PR more than 3 months to discuss that or other things.
During these 3 months and more, keeping icons or not was discussed. The final decision was to remove them so by default the new UI doesn’t have these icons any more (many modules doesn’t have icons by now and these icons took place). But as some users want these icons, one of the main developers (@Pascal_Obry) made a CSS to let users who want these icons back.
The design of the new UI on darktable 2.7 (dev) couldn’t be compare to the old one as lot of things changed. And the position of icons couldn’t easily be adapted.
And as all changes, changes couldn’t make all users happy ! So it’s all about compromises.
See here for more info on the new UI : New interface in darktable 2.7 (dev)