style.css

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
  font-family: sans-serif;
}

main {
  display: flex;
  align-items: center;
  flex-direction: column;
  overflow: hidden;
  min-height: 100vh;
  background: linear-gradient(to left, rebeccapurple, teal);
  user-select: none;
}

#game {
  position: relative;
}

#startScreen {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background: url("/background/nebula1.png");
  background-repeat: no-repeat;
  background-size: cover;

  display: flex;
  align-items: center;
  justify-content: center;
  flex-direction: column;
  backdrop-filter: blur(4px);
  padding-inline: 2rem;
}

#startGameBtn {
  width: 100%;
  font-size: 1.25rem;
  color: white;
  background-color: transparent;
  border: 1px solid white;
  border-radius: 8px;
  backdrop-filter: blur(4px);
  box-shadow: 0 0 12px 1px #0007;
  letter-spacing: 4px;
}
#startGameBtn:hover {
  cursor: pointer;
}

#playAgainBtn {
  position: absolute;
  left: 50%;
  top: 60%;
  transform: translateX(-50%);
  width: 80%;
  font-size: 1.25rem;
  display: none;
  color: white;
  background-color: transparent;
  backdrop-filter: blur(4px);
  border: 1px solid white;
  text-transform: capitalize;
  border-radius: 8px;
  text-transform: uppercase;
  letter-spacing: 4px;
}
#playAgainBtn:hover {
  cursor: pointer;
}

#canvas {
  display: flex;
  height: 100%;
  max-width: 100%;
  box-shadow: 0 2px 2px 1px #0003;
}

#buttons {
  display: flex;
  column-gap: 1.375rem;
  padding-block-start: 1rem;
}

button {
  width: 100px;
  padding-block: 0.75rem;
  border-radius: 4px;
  text-transform: uppercase;
  font-size: 12px;
  font-weight: 900;
  letter-spacing: 2px;
  background: rebeccapurple;
  border: 1px solid #fff3;
  color: #fff;
  box-shadow: 0 1px 1px 1px #0003;
  text-shadow: 0 2px #0007;
}
#laser {
  background: seagreen;
}

@media (min-width: 769px) {
  #buttons {
    display: none;
  }

  #startscreen {
    padding-inline: 4rem;
  }
}