.box {overflow: hidden}
.item {float: left}
.item:nth-of-type(1) {
  width: calc((100% - 20px) * 1 / 6)
}
.item:nth-of-type(2) {
  width: calc((100% - 20px) * 3 / 6);
  margin: 0 10px
}
.item:nth-of-type(3) {
  width: calc((100% - 20px) * 2 / 6)
}

.box {display: flex;}
.item:nth-of-type(1) {flex: 1}
.item:nth-of-type(2) {
  flex: 3;
  margin: 0 10px
}
.item:nth-of-type(3) {flex: 2}

.box {
  display: grid;
  grid-template-columns: 1fr 3fr 2fr;
  grid-gap: 10px
}