可以通过渐变来控制 虚线边框的长度和间隔

[lucyanddarlin]

.border-box{ 
  border: 1px solid transparent;
  background: linear-gradient(white, white) padding-box,
  repeating-linear-gradient(-45deg, #ccc 0, #ccc 0.5em, white 0, white 0.75em);
}