Generated by SassMeister.com.

SassMeister-input-HTML.html

<div class="btn">Upload</div>
<div class="btn--working">gif</div>

SassMeister-input.sass

// ----
// Sass (v3.3.4)
// Compass (v1.0.0.alpha.18)
// ----

.btn
  width: 200px
  font-size: 24px
  line-height: 3
  background-color: green
  color: white
  text-align: center
  border-radius: 3px
  display: inline-block
  
.btn--working
  @extend .btn
  background-color: lightgreen
  width: 50px
  
  

SassMeister-output.css

.btn, .btn--working {
  width: 200px;
  font-size: 24px;
  line-height: 3;
  background-color: green;
  color: white;
  text-align: center;
  border-radius: 3px;
  display: inline-block;
}

.btn--working {
  background-color: lightgreen;
  width: 50px;
}

SassMeister-rendered.html

<div class="btn">Upload</div>
<div class="btn--working">gif</div>