/* style_1.css */

html,
body {
  margin: 0;
  padding: 0;
  height: 100%;
  overflow: hidden; /* スクロールバーを消す（任意） */
}

canvas {
  position: fixed;
  top: 0;
  left: 0;
  width: 100vw;
  height: 100vh;
  z-index: -1; /* canvasを最背面に */
}

.content {
  position: relative;
  z-index: 1; /* canvasより前面に */
  color: white;
  padding: 40px;
  font-family: sans-serif;
}

.start-btn {
  position: absolute;
  left: 50%;
  top: 60vh;       /* ← 画面の60%の高さ：すごく安定する */
  transform: translateX(-50%);
  z-index: 10;

  padding: 20px 40px;
  font-size: 28px;

  background: #64b5f6;
  color: #fff;
  border: none;
  border-radius: 10px;
  cursor: pointer;

  transition: background 0.3s;
}

.start-btn:hover {
  background: #4da4e6;
}

#start-nula {
  position: fixed;
  transform: translateX(-50%);
  z-index: 20;

  width: 260px;
  height: 70px;
  padding: 18px 0;
  font-size: 24px;
  text-align: center;

  background: #64b5f6;
  color: white;
  border: none;
  border-radius: 10px;
  cursor: pointer;
}