metamask-extension/ui/app/components/sidebars/index.scss

.sidebar-right-enter {
  transition: transform 300ms ease-in-out;
  transform: translateX(-100%);
}

.sidebar-right-enter.sidebar-right-enter-active {
  transition: transform 300ms ease-in-out;
  transform: translateX(0%);
}

.sidebar-right-leave {
  transition: transform 200ms ease-out;
  transform: translateX(0%);
}

.sidebar-right-leave.sidebar-right-leave-active {
  transition: transform 200ms ease-out;
  transform: translateX(-100%);
}

.sidebar-left-enter {
  transition: transform 300ms ease-in-out;
  transform: translateX(100%);
}

.sidebar-left-enter.sidebar-left-enter-active {
  transition: transform 300ms ease-in-out;
  transform: translateX(0%);
}

.sidebar-left-leave {
  transition: transform 200ms ease-out;
  transform: translateX(0%);
}

.sidebar-left-leave.sidebar-left-leave-active {
  transition: transform 200ms ease-out;
  transform: translateX(100%);
}

.sidebar-left {
  flex: 1 0 230px;
  background: rgb(250, 250, 250);
  z-index: $sidebar-z-index;
  position: fixed;
  left: 15%;
  right: 0;
  bottom: 0;
  opacity: 1;
  visibility: visible;
  will-change: transform;
  overflow-y: auto;
  box-shadow: rgba(0, 0, 0, .15) 2px 2px 4px;
  width: 85%;
  height: 100%;

  @media screen and (min-width: 769px) {
    width: 408px;
    left: calc(100% - 408px);
  }
}

.sidebar-overlay {
  z-index: $sidebar-overlay-z-index;
  position: fixed;
  height: 100%;
  width: 100%;
  left: 0;
  right: 0;
  bottom: 0;
  opacity: 1;
  visibility: visible;
  background-color: rgba(0, 0, 0, .3);
}