html {
  --crop-mark-thickness: 1px;
  --crop-mark-inset: 20px;
  --crop-mark-length: 10px;
  --crop-mark-gap: 15px;
}

body {
  height: 100dvh;
  margin: 0;
  padding-bottom: 2em;
}

html::before,
html::after,
body::before,
body::after {
  content: "";
  position: fixed;
}

html::before,
html::after {
  width: 100%;
  height: var(--crop-mark-thickness);
  left: 0;
  background: 
    linear-gradient(
      to right,
      
      transparent 
        0
        var(--crop-mark-inset),
      
      black 
        var(--crop-mark-inset)
        calc(var(--crop-mark-inset) + var(--crop-mark-length)),

      transparent
        calc(var(--crop-mark-inset) + var(--crop-mark-length))
        calc(var(--crop-mark-inset) + var(--crop-mark-length) + var(--crop-mark-gap)),
      
      transparent 
        calc(var(--crop-mark-inset) + var(--crop-mark-length) + var(--crop-mark-gap))
        calc(100% - var(--crop-mark-length) - var(--crop-mark-inset) - var(--crop-mark-gap)),

      transparent
        calc(100% - var(--crop-mark-length) - var(--crop-mark-inset) - var(--crop-mark-gap)),
        calc(100% - var(--crop-mark-length) - var(--crop-mark-inset)),
      
      black 
        calc(100% - var(--crop-mark-length) - var(--crop-mark-inset) - var(--crop-mark-gap))
        calc(100% - var(--crop-mark-inset)),
      
      transparent 
        calc(100% - var(--crop-mark-inset))
    );
}

body::before,
body::after {
  height: 100%;
  width: var(--crop-mark-thickness);
  top: 0;
  background: 
    linear-gradient(
      to bottom,
      
      transparent 
        0
        var(--crop-mark-inset),
      
      black 
        var(--crop-mark-inset)
        calc(var(--crop-mark-inset) + var(--crop-mark-length)),

      transparent
        calc(var(--crop-mark-inset) + var(--crop-mark-length))
        calc(var(--crop-mark-inset) + var(--crop-mark-length) + var(--crop-mark-gap)),
      
      transparent 
        calc(var(--crop-mark-inset) + var(--crop-mark-length) + var(--crop-mark-gap))
        calc(100% - var(--crop-mark-length) - var(--crop-mark-inset) - var(--crop-mark-gap)),

      transparent
        calc(100% - var(--crop-mark-length) - var(--crop-mark-inset) - var(--crop-mark-gap)),
        calc(100% - var(--crop-mark-length) - var(--crop-mark-inset)),
      
      black 
        calc(100% - var(--crop-mark-length) - var(--crop-mark-inset) - var(--crop-mark-gap))
        calc(100% - var(--crop-mark-inset)),
      
      transparent 
        calc(100% - var(--crop-mark-inset))
    );
}

html::before {
  top: calc(var(--crop-mark-inset) + var(--crop-mark-length) + var(--crop-mark-gap));
}

html::after {
  bottom: calc(var(--crop-mark-inset) + var(--crop-mark-length) + var(--crop-mark-gap))
}

body::before {
  left: calc(var(--crop-mark-inset) + var(--crop-mark-length) + var(--crop-mark-gap));
}

body::after {
  right: calc(var(--crop-mark-inset) + var(--crop-mark-length) + var(--crop-mark-gap));
}