css 特效

1. 右上角选择效果

DETAILS

.box-wrap {
  width: 200px;
  height: 100px;
  border: 1px solid red;
  position: relative;
}
.box-active:after {
  content: "";
  position: absolute;
  top: 0;
  right: 0;
  border-top: 50px solid #f9f9f9;
  border-left: 50px solid transparent;
}

.box-active:before {
  content: "";
  position: absolute;
  width: 12px;
  height: 8px;
  background: transparent;
  top: 8px;
  right: 4px;
  border: 4px solid #ff0000;
  border-top: none;
  border-right: none;
  transform: rotate(-55deg);
  z-index: 1;
}

55