body {
  font-family: 'Arial', sans-serif;
  background-color: #000;
  margin: 0;
  padding: 0;
  display: flex;
  flex-direction: column;
  height: 100vh;
  color: #fff;
}

header {
  background-color: #222;
  padding: 15px;
  text-align: center;
  display: flex;
  justify-content: space-between;
  align-items: center;
}

header button {
  background-color: #0078d4;
  color: #ffffff;
  padding: 10px 15px;
  border: none;
  border-radius: 5px;
  font-size: 16px;
  cursor: pointer;
  transition: background-color 0.2s;
}

header button:hover {
  background-color: #005ea2;
}

.container {
  flex-grow: 1;
  display: flex;
  flex-direction: column;
  padding: 10px;
}

textarea {
  flex-grow: 1;
  width: 100%;
  border: none;
  padding: 15px;
  font-size: 18px;
  background: #111;
  color: #fff;
  resize: none;
  outline: none;
  line-height: 1.5;
}

/* モバイル対応 */
@media (max-width: 768px) {
  textarea {
    font-size: 16px;
  }
}