select2/docs/_sass/_hamburger.scss

// animated hamburger icon
// @see http://codepen.io/JulienMelissas/pen/LEBGLj

.navbar-toggle {
  border: none;
  background: transparent !important;

  &:hover {
    background: transparent !important;
  }

  .icon-bar {
    width: 22px;
    transition: all 0.2s;
  }

  .top-bar {
    transform: rotate(45deg);
    transform-origin: 10% 10%;
  }

  .middle-bar {
    opacity: 0;
  }

  .bottom-bar {
    transform: rotate(-45deg);
    transform-origin: 10% 90%;
  }

  &.collapsed {
    .top-bar {
      transform: rotate(0);
    }

    .middle-bar {
      opacity: 1;
    }

    .bottom-bar {
      transform: rotate(0);
    }
  }
}