body {
    font-family: 'Noto Sans JP', sans-serif;
    font-size: 13px;
    padding: 30px;
    background: #f7f7f7;
  }
  
  h1 {
    margin-top: 0;
  }
  

  
  .source {
    font-size: 10px;
    color: #888;
  }
  .source a {
    color: #888;
  }
  
  /* Marks */
  .point:hover {
    stroke: #333;
  }
  
  /* Axes */
  .axis line {
    fill: none;
    stroke: #ddd;
    shape-rendering: crispEdges;
  }
  .axis text {
    font-size: 13px;
    fill: #6b6b6b;
  }
  .axis-title {
    font-size: 13px;
    fill: #888;
  }
  .y-axis .tick:first-child line {
    stroke: #b1b1b1;
  }
  .y-axis .tick:first-child text {
    display: none;
  }
  .x-axis .tick:first-child line {
    display: none;
  }
  .axis path {
    display: none;
  }
  
  /* Legend */
  .legend {
    margin: 20px 0;
    list-style: none;
    padding: 0;
  }
  .legend-btn {
    display: inline-block;
    margin: 0 20px 0 0;
    cursor: pointer;
    transition: all ease-in-out 200ms;
  }
  .legend-btn:hover.legend-btn.inactive:hover  {
    opacity: 0.7;
  }
  .legend-btn.inactive {
    opacity: 0.5;
  }
  .legend-symbol {
    width: 12px;
    height: 12px;
    margin-right: 3px;
    display: inline-block;
  }
  .legend-btn[data-difficulty="Easy"] .legend-symbol {
    background: #d3eecd;
  }
  .legend-btn[data-difficulty="Intermediate"] .legend-symbol {
    background: #7bc77e;
  }
  .legend-btn[data-difficulty="Difficult"] .legend-symbol {
    background: #2a8d46;
  }
  
  /* Tooltip */
  #tooltip {
    position: absolute;
    display: none;
    background: #fff;
    box-shadow: 3px 3px 3px 0px rgb(92 92 92 / 0.5);
    border: 1px solid #ddd;
    font-size: 12px;
    font-weight: 500;
    padding: 8px;
    min-width: 160px;
    color: #333;
  }
  .tooltip-title {
    color: #000;
    font-size: 14px;
    font-weight: 600;
  }
  #tooltip ul {
    margin: 5px 0 0 0;
    padding-left: 20px;
  }
  
  /* Scatterplot */
  #scatterplot {
    max-width: 1000px;
  }