Наложение блоков друг на друга

body { 
  margin: 0; 
  padding: 0; 
} 
.black { 
  background-color: black; 
  width: 100%; 
  height: 100px; 
} 
.red { 
  position: relative; 
  top:-50px; 
  width: 200px; 
  height: 50px; 
  background-color: red; 
} 
.red button { 
  position: absolute; 
  width: 50px; 
  height: 20px; 
  top: 15px; 
  margin-left: 10px; 
  border-radius: 10px; 
} 
.red a { 
  position: absolute; 
  top: 15px; 
  left: 85px; 
  text-decoration: none; 
  color: white; 
} 
.red a:hover { 
  text-decoration: underline; 
}

<div class="black"></div> 
<div class="red"> 
  <button>OK</button> 
  <a href="https://www.tut.by/">www.tut.by</a> 
</div>