.menubox {
      border: solid 1px;
      margin-top: 2px;
      margin-left: 10px;
      padding: 10px;
      position: relative;
      background-color:white;
      border-radius: 0.5em;
    }
    hr {
      border-style: none;
      border-top: 1px solid black;
    }
    a.black_color {
      color : black;
      display: block;
      }
    a.white_color {
      color : white;
      display: block;
      }
    .sectionbox {
      border: none;
      margin-top: 2px;
      margin-left: 10px;
      padding: 20px;
      position: relative;
    }
  /* https://developer.mozilla.org/ja/docs/Web/HTML/Element/details */ 
  details {
      border: 1px solid #aaa;
      border-radius: 4px;
      padding: .5em .5em 0;
      background-color:#000033;
      color: white;
  }
  summary {
      font-weight: bold;
      margin: -.5em -.5em 0;
      padding: .5em;
  }
  details[open] {
      padding: .5em;
  }
  details[open] summary {
      border-bottom: 1px solid #aaa;
      margin-bottom: .5em;
  }
  details > hr.divide {
    height: 0.5px;
  }