$green: #4CAF50; // this is our main green color that, let's say, the client really liked

.button-container {
  height: 100%;
  width: 400px;
  font-size: .8rem;
  margin: 0 auto;
  padding: 0;
  display: flex;
  flex-flow: column nowrap;
  align-items: center;
  justify-content: center;
  .btn {
    background-color: $green;
    padding: 5px;
    width: 200px;
    height: 75px;
    margin: 10px;
    line-height: 20px;
    color: white;
    font-weight: bold;
    font-size: 1.7em;
    text-align: center;
    transition: .2s background-color ease-in-out;
    &.lighten:hover {
      background-color: lighten($green, 10%); 
      // On hover, the color changes to #6ec071
    }
    &.darken:hover {
      background-color: darken($green, 10%); 
      // On hover, the color changes to #3d8b40
    }
  }
}