title: CSS change color on scroll / cut text - overflow z-index
body: <p>I want to change the color of a <code>position:fixed</code> menu when scrolling.</p>
  <p><img src="https://i.stack.imgur.com/UTwqh.jpg" alt="enter image description here" /></p>
  <p>My first intention was to use two fixed menus and <code>overflow:hidden</code> but it doesn't work on fixed elements. My second try was using <code>z-index</code>. But it seems impossible.</p>
  <p>Maybe someone has an idea?</p>