Thank you for your efforts. I have tested it and it works as a charm. Was this a general issue or something specific in my configuration ? When I look at the file now, I can see the selection of the attrribute taking place.
Your theme is serving my needs perfectly, it has more features in the front page than I need but these might come in handy in the future. One of the best things this theme also offers opposed to my current theme is the detection of the mobility by Google. My current theme is responsive, but this is not noted by Google 🙁