Short question: where in the main.css is the part for the pulldown menu which appears e.g for the blog-entries in the header-nav?
Which browser do you use? It seems to me that you are not using any developer tools to inspect the DOM and the corresponding CSS?
The image below shows web developer tools in Safari: in the center, you can traverse the DOM, on the left, the corresponding elements of the website are highlighted and on the right, you can see the CSS styles that belong to an element and where in the stylesheet they are defined.
If you are using Chrome, right-click into the window and select “Inspect Element” in the pop-up menu.