styles.css

html,
body {
  margin: 0;
  padding: 0;
  height: 100%;
  width: 100%;
  overflow: hidden;
  user-select: none;
}

.menu {
  position: absolute;
  top: 0;
  right: -180px;
  display: flex;
  width: 200px;
  flex-direction: column;
  transition: right 0.4s;
}

.menu:hover {
  right: 0;
}

.menu input[type="file"] {
  display: none;
}

.menu button {
  border: 1px solid #000;
  margin: 5px 5px 0 0;
  outline: none;
  background: #fff;
  color: #000;
  cursor: pointer;
  padding: 2px;
}

.menu button:hover {
  background: #000;
  color: #fff;
}


.github {
  position: fixed;
  display: block;
  bottom: 0;
  left: -140px;
  right: 0;
  height: 40px;
  background-color: #24292e;
  width: 130px;
  display: flex;
  justify-content: flex-end;
  padding-right: 10px;
  border-radius: 0 10px 0 0;
  text-decoration: none;
  transition: left .3s, width .2s;
}

.github:hover {
  width: 140px;
}

.github:hover .arrow {
  opacity: 1;
  left: 15px;
}


.github span {
  color: #fff;
  margin: auto 10px;
}

.github svg {
  margin: auto 0;
}

.github svg path {
  fill: #fff;
}

.github .arrow {
  position: absolute;
  left: 0;
  width: 15px;
  height: 15px;
  top: 50%;
  transform: translateY(-50%);
  opacity: 0;
  transition: opacity .3s, left .2s;
}

.github .arrow::after, .github .arrow::before {
  content: '';
  display: block;
  width: 50%;
  height: 2px;
  background-color: #fff;
  position: absolute;
}

.github .arrow::after {
  transform: rotate(45deg);
  top: 4px;
}

.github .arrow::before {
  transform: rotate(-45deg);
  bottom: 4px;
}