<a href="" class="cs-button-4" aria-label="prenota ora">Prenota Ora</a>

.cs-button-4 {
    text-align: center;
    font-size: 1rem;
    line-height: clamp(2.875rem, 8vw, 3.5rem);
    text-decoration: none;
    font-weight: 700;
    min-width: 10.875rem;
    margin: 0;
    overflow: hidden;
    color: #fff;
    padding: 0 3rem;
    box-sizing: border-box;
    background-color: #1a1a1a;
    display: inline-block;
    position: relative;
    z-index: 1;
  }
  .cs-button-4:before {
    content: '';
    width: 150%;
    height: 110%;
    background: var(--primary);
    opacity: 1;
    position: absolute;
    display: block;
    top: 50%;
    left: -130%;
    z-index: -2;
    transform: skew(45deg) translateY(-50%);
    transition: left .3s;
  }
  .cs-button-4:hover:before {
    left: -20%;
  }
}