index.css

* {
  margin: 0;
  padding: 0;
}

html, body {
  width: 100%;
  height: 100%;
}

body {
  display: flex;
  justify-content: center;
  align-items: center;
  position: relative;
  background-image: url('./image.png');
  background-size: cover;
  background-repeat: no-repeat;
  background-position: center;
}

.button {
  display: block;
  padding: 10px 20px;
  background: linear-gradient(to bottom, #a8e6b8 0%, #3e9652 36%, #276b15 45%, #000000 100%);
  border-radius: 10px;
  border: 1px solid #363636;
  box-shadow: 0px 1px 3px rgba(000,000,000,0.5), inset 0px 0px 1px rgba(255,255,255,0.6);
  color: #ffffff;
  font-family: Arial, Helvetica, sans-serif;
  font-size: 14px;
  text-decoration: none;
  text-shadow: 0px -1px 0px rgba(000,000,000,1), 0px 1px 0px rgba(255,255,255,0.2);
}

.button:active {
  margin-top: 3px;
  margin-left: 3px;
  opacity: 0.8;
}

.credit {
  position: absolute;
  right: 8px;
  bottom: 8px;
  padding: 0 0 0 8px;
  color: #fff;
  font-size: 8px;
  opacity: .8;
}

.credit a {
  color: #fff;
  opacity: .6;
}