I'm making a pure CSS animated navbar using the checkbox as a hamburger menu toggler, changing various elements with :checked and the + selector, which I've gotten to work on grand-child elements, but not siblings, I haven't found an adequate solution on the web either. Here's my HTML code, obviously stripped down a little:
.toggler:checked+.menu {
  width: 350px;
}<div class="menu">
  <div class="menu-background"></div>
  <div class="menu-navigation"></div>
</div>
<input type="checkbox" class="toggler">
<div class="hamburger">I got it to work on children of the hamburger class, so I'm fairy confident its an issue with the selector
 
     
     
     
    