<img src="//www.w3cplus.com/sites/default/files/blogs/2022/2207/avatar.svg" alt="">
<div class="gradient"></div>

<div class="target"></div>

<div class="source">
  <img src="//www.w3cplus.com/sites/default/files/blogs/2022/2207/avatar.svg" alt="">
  <div class="gradient"></div>
</div>

<div class="form">

  <label for="opacity">--opacity:</label>
  <input type="range" min="0" max="100" step="1" value="30" name="opacity" id="opacity">
  <output id="opacity-output">30%</output>
</div>

@import url("https://fonts.googleapis.com/css2?family=Exo:wght@600&display=swap");

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body {
  width: 100vw;
  min-height: 100vh;
  font-family: "Exo", Arial, sans-serif;
  background-color: #557;
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(min(100%, 160px), 1fr));
  gap: 1rem;
  padding: 1rem;
  place-content: center;
}

body > * {
  width: 100%;
}

img {
  display: block;
  aspect-ratio: 3 / 4;
}

.gradient {
  aspect-ratio: 3 / 4;
  background-image: linear-gradient(to bottom, #09f, #90f);
}

:root {
  --opacity: 30%;
}

.target {
  aspect-ratio: 3 / 4;
  background-image: -webkit-cross-fade(
    url("//www.w3cplus.com/sites/default/files/blogs/2022/2207/avatar.svg"),
    linear-gradient(to bottom, #09f, #90f),
    var(--opacity)
  );
  background-size: 100% 100%;
}

.source {
  position: relative;
  aspect-ratio: 3 / 4;
}

.source > * {
  position: absolute;
  top: 0;
  right: 0;
  bottom: 0;
  left: 0;
}

.source > img {
  z-index: 1;
  width: 100%;
  height: 100%;
}

.source > .gradient {
  z-index: 2;
  opacity: var(--opacity);
}

.form {
  padding: 1rem;
  background-color: rgb(0 0 0 / 0.6);
  backdrop-filter: blur(20px);
  position: fixed;
  bottom: 0;
  left: 0;
  right: 0;
  display: flex;
  justify-content: center;
  align-items: center;
  gap: 10px;
  color: #fff;
  z-index: 99;
}

.form input {
  width: 32px;
  outline: none;
  border: none 0;
  font-family: "Exo", Arial, sans-serif;
  background-color: transparent;
}

.form label {
  line-height: 1;
  display: inline-flex;
  align-items: center;
}

input[type="range"] {
  width: min(200px, 10vh);
}

const rootElement = document.documentElement;
const inputHander = document.getElementById("opacity");
const outPut = document.getElementById("opacity-output");

inputHander.addEventListener("input", (etv) => {
  rootElement.style.setProperty("--opacity", `${etv.target.value}%`);
  outPut.textContent = `${etv.target.value}%`;
});