<div class="text">
  <strong class="text__title">
    Большой-большой <br />
    текст
  </strong>
  И ещё текст поменьше
</div>

.text {
  display: inline-block;
  font-size: 30px;
  font-weight: 700;
  color: transparent;
  background: #222;
  -webkit-background-clip: text;
}

.text__title {
  display: block;
  font-size: 60px;
}

const text = document.querySelector('.text');

text.addEventListener('mousemove', (e) => {
  const x = e.offsetX / e.target.offsetWidth * 100;
  const y = e.offsetY / e.target.offsetHeight * 100;
  text.style.backgroundImage = `radial-gradient(100px at ${x}% ${y}%, #0081cc 0%, #0081cc 99%, #222 100%)`;
})