.block1
  .container
    button.btn Text
      .dropdown
      
.block2
  .container
    button.btn Text
      .dropdown

* {
  box-sizing: border-box;
}

.block1, .block2 {
  padding: 20px;
  margin: 20px;
  width: calc(100% - 40px);
  background: #e6e6e6;
}

.block2 {
    background: #a1a1a1;
}


.dropdown {
  width: 40px;
  background: skyblue;
  height: 100px;
  position: absolute;
  left: 0;
  border: 1px solid red;
  z-index: 30;
}

.block1 .dropdown {
  top: 0;
  left: 50px;
}

.block2 .dropdown {
  bottom: 0;
  background: yellowgreen;
}

.btn {
  position: relative;
  z-index: 0;
}