css to implement four-corner border style

The effect is as shown in the figure
This picture only implements the lower left and lower right corner styles
The same goes for the upper right and upper left

/*  容器 */
.card-mini {
  position: relative;
}
/*  左下*/
.card-mini::before {
  content: '';
  position: absolute;
  left: 0;
  bottom: 0;
  width: 20px;
  height: 20px;
  border-bottom: 2px solid #253d64;
  border-left: 2px solid #253d64;
  border-bottom-left-radius: 10px;
}
/*  右下*/
.card-mini::after {
  content: '';
  position: absolute;
  right: 0;
  bottom: 0;
  width: 20px;
  height: 20px;
  border-bottom: 2px solid #253d64;
  border-right: 2px solid #253d64;
  border-bottom-right-radius: 10px;
}

Upper right and upper left. Change bottom to top.

.card-mini::before {
  content: '';
  position: absolute;
  left: 0;
  top: 0;
  width: 20px;
  height: 20px;
  border-top: 2px solid #253d64;
  border-left: 2px solid #253d64;
  border-top-left-radius: 10px;
}
.card-mini::after {
  content: '';
  position: absolute;
  right: 0;
  top: 0;
  width: 20px;
  height: 20px;
  border-top: 2px solid #253d64;
  border-right: 2px solid #253d64;
  border-top-right-radius: 10px;
}