html {
  font-family: sans-serif;
}

button {
  width: 150px;
  margin: auto;
  line-height: 2;
  font-size: 1.1rem;
  text-align: center;
  color: white;
  text-shadow: 1px 1px 1px black;
  border-radius: 20px / 15px;
  border: none;
  cursor: pointer;

  background-color: #ff0000;
  background-color: rgba(255,0,0,1);
  box-shadow: inset 1px 1px 3px rgba(255,255,255,0.4),
              inset -1px -1px 3px rgba(0,0,0,0.4);
}

button:hover {
  background-color: rgba(255,0,0,0.5);
}

button:active {
  box-shadow: inset 1px 1px 3px rgba(0,0,0,0.4),
              inset -1px -1px 3px rgba(255,255,255,0.4);
}

body {
  display: -webkit-box;
  display: -ms-flexbox;
  display: flex;
}