Navigation and drop down menu items

Hello!

I am trying to change the size and opacity of my dropdown menu items, so that the box fits the width of the text and the black background is only slightly visible.

I used these two codes found in the forum, but nothing changed:

.header-nav .header-nav-item--folder .header-nav-folder-content {
  width: auto;
}
.subnav {background-color: rgba(0,0,255,0.1) !important;}

Hi. Can you share link to your site? We can help easier