Show button on Hover

  <div class="container">
    <div class="cards-container">
      <div class="card">
        <div class="elms-animation">
          <span class="one"></span>
          <span class="two"></span>
          <span class="three"></span>
          <span class="four"></span>
        </div>
        <img src="https://images.unsplash.com/photo-1647036003499-94eebb3388c7?ixlib=rb-1.2.1&ixid=MnwxMjA3fDB8MHxlZGl0b3JpYWwtZmVlZHw0M3x8fGVufDB8fHx8&auto=format&fit=crop&w=500&q=60" alt=""/>
        <div class="content">
          <button>Discover</button>
        </div>
      </div>
      <div class="card">
        <div class="elms-animation">
          <span class="one"></span>
          <span class="two"></span>
          <span class="three"></span>
          <span class="four"></span>
        </div>
        <img src="https://images.unsplash.com/photo-1586348943529-beaae6c28db9?ixlib=rb-1.2.1&ixid=MnwxMjA3fDB8MHxzZWFyY2h8M3x8bmF0dXJlfGVufDB8MXwwfHw%3D&auto=format&fit=crop&w=500&q=60" alt=""/>
        <div class="content">
          <button>Discover</button>
        </div>
      </div>
      <div class="card">
        <div class="elms-animation">
          <span class="one"></span>
          <span class="two"></span>
          <span class="three"></span>
          <span class="four"></span>
        </div>
        <img src="https://images.unsplash.com/photo-1414609245224-afa02bfb3fda?ixlib=rb-1.2.1&ixid=MnwxMjA3fDB8MHxzZWFyY2h8MTF8fG5hdHVyZXxlbnwwfDF8MHx8&auto=format&fit=crop&w=500&q=60" alt=""/>
        <div class="content">
          <button>Discover</button>
        </div>
      </div>
    </div>
  </div>

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}
body {
  background-color: lightsteelblue;
}

.card .content {
  display: flex;
  justify-content: center;
  align-items: center;
}

.container {
  max-width: 900px;
  margin-left: auto;
  margin-right: auto;
  padding: 30px 0;
}
.cards-container {
  height: 100vh;
  display: flex;
  align-items: center;
  justify-content: space-around;
  flex-wrap: wrap;
  padding-left: 15px;
  padding-right: 15px;
}

.card {
  max-width: 300px;
  height: 400px;
  position: relative;
  box-shadow: 0 0 15px rgba(0, 0, 0, .2);
  margin: 25px 0;
  width: 30%;
}

@media screen and (max-width: 700px) {
  .card {
    width: 45%;
  }
}
@media screen and (max-width: 500px) {
  .card {
    width: 90%;
  }
}
.card .elms-animation,
.card .content {
  position: absolute;
  top: 0;
  left: 0;
  height: 100%;
  width: 100%;
}
.card .elms-animation {
  z-index: 5;
}
.card .elms-animation span {
  position: absolute;
  background-color: rgba(0, 0, 0, .6);
  height: 0;
  width: 0;
  transition: all .5s ease-out;
}
.card .elms-animation span.one {
  top: 0; left: 0;
}
.card .elms-animation span.two {
  top: 0; right: 0;
}
.card .elms-animation span.three {
  left: 0; bottom: 0;
}
.card .elms-animation span.four {
  right: 0; bottom: 0;
}

.card:hover .elms-animation span {
  width: 50%;
  height: 50%;
}

.card img {
  height: 100%;
  width: 100%;
  object-fit: cover;
  object-position: center;
  display: block;
}

.card .content {
  z-index: 6;
  visibility: hidden;
}
.card:hover .content {
  animation: show .3s .4s linear forwards;
}
.card .content button {
  padding: .6rem 1.3rem;
  border: 3px solid #FFF;
  background: transparent;
  color: #FFF;
  font-size: 1rem;
  outline: none;
  cursor: pointer;
  transition: background .3s ease;
}
.card .content button:hover {
  background: #FFF;
  color: #333;
}

@keyframes show {
  to {
    visibility: visible;
  }
}