<a href="#" class="btn01">Button</a>

.btn01 {
  display:block;  
  max-width: 180px;
  border: 2px solid #333;
  font-size: 16px;
  color: #333;
  font-weight: bold;
  padding:16px;
  text-align: center;
  border-radius: 4px;
  transition: .4s;
}
.btn01:hover {
  background-color: #333;
  border-color: #333;
  color: #FFF;
}

背景色を変更する

<a href="#" class="btn02">Button</a>

.btn02 {
  display:block;  
  max-width: 180px;
  background-color: #333;
  font-size: 16px;
  color: #FFF;
  font-weight: bold;
  padding:16px;
  text-align: center;
  border-radius: 4px;
  transition: .4s;
}
.btn02:hover {
  background-color: #D3BA2B;
}