body {
  background: url("https://media.istockphoto.com/id/506692747/photo/artificial-grass.jpg?s=612x612&w=0&k=20&c=y5I6l-1MgmlPzf2DcEYX08dTLkUXgeo8PGa8Jv3EaOU=") no-repeat center center fixed;
  background-size: cover;
  font-family: Arial, sans-serif;
}

#canvas {
  border: 5px solid green;
  margin: 20px auto;
  display: block;
}

#score {
  font-size: 48px;
  font-weight: bold;
  color: white;
  text-align: center;
  margin: 10px auto;
  display: block;
}

#start {
  font-size: 18px;
  padding: 10px;
  border-radius: 10px;
  border: none;
  background: green;
  color: white;
  text-align: center;
  margin: 10px auto;
  display: block;
}

.score-text {
  color: white;
  font-size: 60px;
  text-align: center; 
}

div { /* added this selector */
  display: inline-block; /* added this property */
}