.ac {
  margin: 0 auto;
}
.ac-parent {
  position: relative;
  height: 50px;
  line-height: 50px;
  text-align: center;
  border-bottom: 1px solid #595757;
  cursor: pointer;
  transition: .3s;
  font-size: 16px;
  font-weight: bold;
}
.ac-parent:before {
  content: "";
  position: absolute;
  top: 50%;
  right: 8px;
  transform: translateY(-50%);
  /*横線*/
  width: 16px;
  height: 2px;
  background: #231815;
}
.ac-parent:after {
  content: "";
  position: absolute;
  top: 50%;
  /* 8px+12px-1px(幅2pxの半分) */
  right: 15px;
  transform: translateY(-50%);
  transition: all .3s;
  /*縦線*/
  width: 2px;
  height: 16px;
  background: #231815;
}
.ac-parent.open:after {
  top: 25%;
  transform: rotate(90deg);
  opacity: 0;
}
.ac-child {
}
.ac-child table {
  width: 100%;
  margin-top: 6px;
}
.ac-child table:not(:first-child) {
  margin-top: 12px;
}
.ac-child table thead th {
  width: 100%;
  height: 36px;
  line-height: 36px;
  text-align: center;
  border-bottom: 1px solid #595757;
  font-weight: normal;
  font-size: 14px;
}
.ac-child table tbody tr:nth-child(odd) {
  background-color: #efefef;
}
.ac-child table tbody tr:nth-child(even) {
  background-color: #f7f8f8;
} 
.ac-child table tbody tr td {
  padding: 0.5em;
  font-size: 14px;
}
.ac-child table tbody tr td:nth-child(2) {
  border-left: 1px solid #ccc;
}

.annotation {
  margin-top: 12px;
}
.annotation li {
  font-size: 14px;
  padding-left: 1em;
  text-indent: -1em;
  line-height: 1.6;
  margin-top: 8px;
}