<button class="btn">
  <img src="https://assets.codepen.io/1425525/379536_bell_icon.png" class="mr-10" />
  <p class="btn-scale-hover">Это абсолютно бесплатно</p>
</button>

body {
  display: flex;
  align-items: center;
  justify-content: center;

  height: 100vh;
  margin: 0;
  overflow: hidden;

  font-family: sans-serif;
}

.btn {
  display: flex;
  align-items: center;
  padding: 10px 30px;
  border: none;
  
  color: #212529;
  background: transparent;
  cursor: pointer;
}

.mr-10 {
  margin-right: 10px;
}

.btn-scale-hover {
  padding: 10px;
  
  transform: scaleX(0);
  transform-origin: left top;
  
  color: #fff;
  background: #47cf73;
  
  transition: 1s;
}

.btn img:hover ~ .btn-scale-hover {
  transform: scaleX(1);
}