What is the fine-grained topic of the following text: Theis & Khan, the appointed architect, design approach at 76 Portland Place was to create a sustainable and flexible working environment within the confines of the existing 1950s building, the fluidity of this new working environment is in direct contrast to the formality of the current headquarters building. Only return the topic.
Theis & Khan's sustainable and flexible design approach for 76 Portland Place.