User:Star0/sandbox/styles.css

.CCsingle {
  position: relative;
}

.CCsingle::after {
  content: '';
  position: absolute;
  top: 0;
  right: 0;
  width: 25%;
  height: 25%;
  clip-path: polygon(100% 0, 0 0, 100% 100%);
}

.CCsingle-byd::after {
  background-color: #bd030e; /* byd颜色 */
}

.CCsingle-etr::after {
  background-color: #502f74; /* etr颜色 */
}

.CCsingle-ftr::after {
  /*background-color: #9a337a;*/
}

.CCsingle-prs::after {
  background-color: #b3cc54; /* prs颜色 */
}