.header_bg {
    background: #323232;
    width: 100%;
    height: 80px;
  }
  
  .header_contents {
    width: 100%;
    max-width: 1024px;
    height: 100%;
    margin: 0 auto;
    display: flex;
    justify-content: space-between;
    align-items: center;
  }
  
  .header_contents h1 {
    font-size: 22px;
    margin: 0 0 0 40px;
  }
  
  .header_nav_lists {
    display: flex;
  }
  
  .header_nav_lists li {
    margin: 0 40px 0 0;
  }
  
  .nav_link {
    font-size: 18px;
  }
  
  /* Responsive menu button */
  .responsive_btn {
    display: none;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    width: 32px;
    height: 32px;
    margin: 0 40px 0 0;
    cursor: pointer;
    position: relative;
    z-index: 9999;
  }
  
  .menu_line {
    background: #000000;
    border-radius: 5px;
    width: 100%;
    height: 5px;
    margin: 4px 0;
  }
  
  /* Responsive style */
  @media screen and (max-width: 1020px) {
    .responsive_btn {
      display: flex;
    }
  
    .header_bg {
      position: relative;
    }
  
    .header_nav {
      display: block;
      background: #ffffff;
      width: 100%;
      height: 100vh;
      padding: 80px 0 0 0;
      position: fixed;
      top: 0;
      right: -100%;
      transition: .5s;
      z-index: 9998;
    }
  
    .header_nav_lists {
      display: block;
      text-align: center;
    }
  
    .header_nav_lists li {
      margin: 0 0 40px;
      text-align: center;
    }
  
    .nav_link {
      font-size: 20px;
    }

    /* 追加: ハンバーガーメニュー内リンクの文字サイズを拡大 */
    .header_nav a { font-size: 18px; }
  }
  
  /* js function "menuToggle" starting only */
  .header_nav.menu_active {
    right: 0;
  }