We have been thinking about the idea of updating the Qt Creator GUI with a more contemporary flat style design, and adding a Light theme in addition to the current Default and Dark themes. Moreover, all the icons in the UI would be simplified and become consistently unified under the same style.
Down below are a couple of screenshots with examples of what these new designs would look like. They are an early concept, so it we'd love to get useful feedback from you to take this forward!
And here are a couple of PDF documents with further examples of the new designs: