Animation problems

Well I have a problem in the responsiveness of my web page due to navbar. In navbar when the screen is less than 540px wide the navbar gets the dropdown but my problem is that the content of the dropdown is superimposed by another div as you can see here

link

I tried to put the position of the div in relative and it turns out but all the animations that I have in the page are without animations, like this:

.dropdown-content {
   position: absolute;
   width: 100%;
   z-index: 1;
}
.artigos_para_venda{
   z-index: -1;
   position: relative;
}

link

Does anyone know how to solve it?