CSS checkbox: click one label, change two things inside one button

I looked at similar posts, but they use JavaScript. I need to use HTML and CSS only.

How can I make a two labels change with the click of one label? (I think that's the process.)

This is for a button in a navigation bar that 1) changes from "Main >" to "Directory <" on click, then 2) toggles a drop-down box that floats above the body content. 3) Clicking "Main" will direct to the "Main" page, clicking ">" will toggle the button to change to "Directory <", clicking "Directory" will open the drop-down and clicking "<" will change to button back to "Main >" (closing the drop-down box if open).

I can't show the code I have right now because it's an embarrassing beginner mess in its early stage. Suggest away!