How to invert stroke text color depending on background

Question

I have 2 divs 50% width each. There is a huge header h1 which should have the color of these two divs. I have tried mix-blend-mode but it gives me some random colors when se

Answer 1

One idea is to duplicate the text and use CSS variable to define the color so you can easily change them in one place. I used clip-path to hide half of one text and show the other half:

body {
  margin: 0;
  --c1:#510035;
  --c2:#E8E8E8;
}
body:hover {
  --c1:red;
  --c2:blue;
}

h1 {
  font-size: 4.7em;
  text-transform: uppercase;
  margin: 0;
}
.first {
  background:var(--c1);
  -webkit-text-stroke: 3px var(--c2);
}

.second {
  background:var(--c2);
  -webkit-text-stroke: 3px var(--c1);
  clip-path:polygon(0% 0%, 50% 0%, 50% 100%,0% 100%);
}

.lp-header {
  position:absolute;
  top:0;
  left:0;
  right:0;
  min-height:100vh;
  box-sizing:border-box;
  color: transparent;
  z-index: 1;
  padding: 50px;
  text-align: center;
  transition:0.5s;
}

<h1 class="lp-header first">left or right</h1>
<h1 class="lp-header second">left or right</h1>