style.css

html {
  height: 100%;
}

body {
  margin: 0;
  padding: 0;
  width: 100%;
  height: 100%;
  background: #f9f8e9;
}

main {
  position: absolute;
  top: 180px;
  left: 50%;
  transform: translateX(-50%) translateY(-50%);
  width: 320px;
  height: 150px;
  display: flex;
  justify-content: center;
  flex-flow: column;
  align-items: center;
  background-color: rgba(255, 255, 255, .9);
  border-radius: 3px;
  box-shadow: 0 1px 10px rgba(0, 0, 0, .2);
}

h1 {
  font-size: 20px;
  font-weight: bold;
  color: #31494e;
  margin-top: 0;
}

ul {
  display: flex;
  justify-content: center;
  list-style: none;
  margin: 0;
  padding: 0;
}

li .button {
  display: block;
  text-decoration: none;
  color: #33634f;
  background-color: #aeefc4;
  cursor: pointer;
  transition: all .1s ease;
  padding: 10px 20px;
  font-size: 20px;
  border-radius: 4px;
}

li .button:not(.start):not(.pause) {
  background-color: #eee;
  cursor: default;
  transition: none;
}

.button:before {
  display: inline;
  text-transform: capitalize;
}

.button.start:before {
  content: "start"
}

.button.pause:before {
  content: "pause"
}

.button:not(.start):not(.pause):before {
  content: "...loading"
}

.button.start:hover,
.button.pause:hover {
  opacity: 0.7;
}