<div class="one">one</div>
<div class="two">two</div>
<div class="anchored">I am anchored to two elements</div>

.one,
.two {
  position: absolute;
  padding: 1rem;
  border: 2px solid;
  background: gold;
}

.one {
  anchor-name: --one;
}

.two {
  anchor-name: --two;
  bottom: 0;
  right: 0;
}

.anchored {
  position: absolute;
  top: anchor(--one bottom);
  left: anchor(--one right);
  right: anchor(--two left);
  bottom: anchor(--two top);
  display: grid;
  place-items: center;
}

body {
  height: 100dvh;
  font-family: system-ui;
  font-size: 18px;
  margin: 0;
}

.anchored {
  background: skyblue;
}