<div class="container">
  <a class="btn">Кнопка 1</a>
  <a class="btn">Кнопка 2</a>
  <a class="btn">Кнопка 3</a>
  <a class="btn">Кнопка 4</a>
  <a class="btn">Кнопка 5</a>
</div>

body {
  display: flex;
  justify-content: center;
  align-items: center;
  flex-direction: column;
  gap: 80px;
  min-height: 100vh;
  background: linear-gradient(to bottom, #fff9ff, #ffe5b1);
  font-family: tahoma;
  padding: 0;
  margin: 0;
}

.container {
  width: 70%;
  box-sizing: border-box;
  padding: 50px;
  background-color: orange;
  display: flex;
  justify-content:center;
  align-items: center;
  flex-direction: column;
  position: relative;
  z-index: 0;
  border-radius: 10px;
  gap: 10px;
}

.btn {
  text-align: center;
  background-color: #603d11;
  padding: 20px 40px;
  border-radius: 10px;
  cursor: pointer;
  display: block;
  color: #fff;
  text-transform: uppercase;
  transition: .2s all;
  position: relative;
  z-index: 0;
}

.btn:after {
  content: "";
  display: block;
  position: absolute;
  left: 0;
  right: 0;
  top: -5px;
  bottom: -5px;
  z-index: -1;
}

/* Вся магия тут */
/* All the magic is here */

.container:has(.btn:hover) .btn:not(:hover) {
  opacity: .5;
}