.icon-silver {
  position: relative;
  display: inline-block;
  color: #c0c0c0; /* tono base plata */
  background: linear-gradient(
    120deg,
    #b0b0b0 20%,
    #e0e0e0 40%,
    #f8f8f8 50%,
    #d0d0d0 60%,
    #b0b0b0 80%
  );
  background-size: 200% 200%;
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  animation: shine 3s linear infinite;
}

@keyframes shine {
  0% { background-position: 200% 0; }
  100% { background-position: -200% 0; }
}

.btn-negro-destello {
  position: relative;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: .5rem;
  padding: .85rem 1.25rem;
  border-radius: .75rem;
  font-weight: 600;
  letter-spacing: .2px;
  color: #f5f5f5;
  background: #0a0a0a; /* negro sólido */
  border: 1px solid #1a1a1a;
  box-shadow: inset 0 1px 0 rgba(255,255,255,.05),
              0 6px 14px rgba(0,0,0,.45);
  overflow: hidden;
  transition: transform .2s ease, box-shadow .2s ease;
}

/* Capa del destello */
.btn-negro-destello::after {
  content:"";
  position:absolute;
  top:0; left:-50%;
  width:40%; height:100%;
  background: linear-gradient(
    120deg,
    transparent 0%,
    rgba(255,255,255,.4) 50%,
    transparent 100%
  );
  transform: skewX(-20deg);
  opacity: 0;
  pointer-events: none;
}

/* Hover → activa ida y vuelta */
.btn-negro-destello:hover::after {
  opacity: 1;
  animation: rayo-plata 1.6s ease-in-out forwards;
}

@keyframes rayo-plata {
  0%   { left:-50%; opacity:0; }
  15%  { opacity:1; }
  50%  { left:120%; opacity:0.6; }
  85%  { opacity:1; }
  100% { left:-50%; opacity:0; }
}