Switch child theme from Antimatter to Quark



I have created a child theme of antimatter using this tutorial here : https://learn.getgrav.org/themes/customization#theme-inheritance

I want to switch to Quark. Antimatter and quark have basically the same pages templates with same name. I just changed antimatter to quark in step 2 and 5, but it’s not working, i have the page only with html and no css is taken into account.

Why is that ? How can i switch easily to quark ? Thanks in advance