header {
  background-color: #f8f8f8;
  padding: 1em;
  border-bottom: 1px solid #eee;
}

header nav {
  display: flex;
  justify-content: space-between;
  align-items: center;
}

header h1 a {
  text-decoration: none;
  color: #333;
  font-size: 1.5em;
}

/* ハンバーガーメニューのスタイル */
.hamburger-menu {
  position: relative;
  display: inline-block;
}

.hamburger-icon {
  display: flex;
  flex-direction: column;
  justify-content: space-around;
  width: 30px;
  height: 25px;
  background: transparent;
  border: none;
  cursor: pointer;
  padding: 0;
  box-sizing: border-box;
}

.hamburger-icon span {
  display: block;
  width: 100%;
  height: 3px;
  background-color: #333;
  border-radius: 3px;
  transition: all 0.3s ease-in-out;
}

.menu-items {
  display: block; /* 追加 */
  visibility: hidden;
  opacity: 0;
  transition: visibility 0s, opacity 0.3s ease-in-out;
  position: absolute;
  top: 100%;
  right: 0;
  background-color: #f8f8f8;
  border: 1px solid #eee;
  list-style: none;
  padding: 0;
  margin: 0;
  min-width: 150px;
  z-index: 1000;
}

.menu-items.is-active {
  visibility: visible;
  opacity: 1;
}

.menu-items li {
  padding: 0.5em 1em;
}

.menu-items li a,
.menu-items li form input[type="submit"] {
  text-decoration: none;
  color: #007bff;
  background: none;
  border: none;
  padding: 0;
  font: inherit;
  cursor: pointer;
  display: block; /* リンク全体をクリック可能にする */
  width: 100%;
  text-align: left;
}

.menu-items li a:hover,
.menu-items li form input[type="submit"]:hover {
  background-color: #e9e9e9;
}

/* ナビゲーションバーの既存のul要素は不要になるため削除 */
header nav ul {
  display: none; /* 既存のulを非表示にする */
}