.card-group{
  margin-left: auto;
  margin-right: auto;
  max-width: 700px;
  width: 90%;
  height: auto;
   /* ポイント１ */
  display: flex;
  flex-direction: row;
  flex-wrap: wrap;
  justify-content: flex-start;
}
/* ポイント２ */
.card-group > :nth-child(2n){
  margin-left: 20px;
}
/* ポイント３ */
.card-group > :nth-child(n+3){
  margin-top: 20px;
}
.card{
  /* ポイント４ */
  width: calc((100% - 20px * 1) / 2);
  height: auto;
  border-radius: 8px;
  overflow: hidden;
  box-shadow: 0 4px 15px rgba(0,0,0,.2)
}
.card__imgframe{
  width: 100%;
  height: auto;
  padding-top: 56.25%;
  background: #bbb;
  box-sizing: border-box;
}
.card__textbox{
  width: 100%;
  height: auto;
  padding: 20px 18px;
  background: #fff;
  box-sizing: border-box;
}
.card__textbox > * + *{
  margin-top: 10px;
}
.card__titletext{
  font-size: 20px;
  font-weight: bold;
  line-height: 125%;
}
.card__overviewtext{
  font-size: 12px;
  line-height: 150%;
}