I think you fell for a common misunderstanding about the nth-child selector
#yourid:nth-child(2n) does NOT mean "select the nth child of the element with id=yourid"
It means: Select all elements with id=yourid (there can be only one!) and then filter those elements so that only those elements remain that are themselves the correct nth-child of their parents.
On top of that: Every id attribute on the same page can appear only once! You chose to use the same id="article-inspir" for several <article> elements which is illegal. So you should go for class="article-inspir" instead and change the selector to ".article-inspir"