CSS
html {
  scroll-behavior: smooth;
}
.banner_on {
  height: 50vh;
  width: 100%;
  background: #acc;
  display: grid;
  place-content: center;
}

.fixed-content {
  position: fixed;
  width: 80%;
  top: 0;
  left: 50%;
  transform: translateX(-50%);
  pointer-events: all;
  z-index: 2;
  background: #7777;
  text-align: center;
  display: block;
  padding-block: 1em;
}
.banner_off {
  height: 100vh;
  background: #cac;
  display: grid;
  place-content: center;
}

.hidden {
  animation: fade 0.3s ease-in-out forwards;
  pointer-events: none;
}
@keyframes fade {
  from {
    opacity: 1;
  }

  to {
    opacity: 0;
  }
}

.visible {
  animation: fadeOut 0.2s ease-in-out forwards;
  pointer-events: all;
}

@keyframes fadeOut {
  from {
    opacity: 0;
  }
  to {
    opacity: 1;
  }
}

          

script
const fixedElement = document.querySelector(".fixed-content");
const targetElement = document.querySelector(".banner_off");
let isHidden = false;
window.addEventListener("scroll", () => {
  const fixedElementRect = fixedElement.getBoundingClientRect();
  const targetElementRect = targetElement.getBoundingClientRect();

  if ((fixedElementRect.bottom >= targetElementRect.top) & (fixedElementRect.top <= targetElementRect.bottom)) {
    if (!isHidden) {
      fixedElement.classList.remove("visible");
      fixedElement.classList.add("hidden");
      isHidden = true;
    }
  } else {
    if (isHidden) {
      fixedElement.classList.add("visible");
      fixedElement.classList.remove("hidden");
      isHidden = false;
    }
  }
});