Bleed area

In printing, the bleed area is the portion of the printed document that extends beyond the trim edge. It is added to the document to ensure that there are no white margins or unfinished edges when the document is trimmed to its final size.

When a document has a bleed, it means that the ink or color extends beyond the trim edge of the page and into the bleed area. This allows the printer to trim the document to its final size without leaving any unprinted areas on the edges.

The bleed can be added using the bleed property inside a @page at-rule.

@page {
    size: A4;
    margin: 10mm;
    bleed: 10mm;
    background: red;
}

Marks

@page {
    size: A4;
    margin: 10mm;
    bleed: 10mm;
    /* Add one or more marks */
    marks: cross crop colors;
}

Crop Marks

Crop marks, also known as trim marks, are lines printed on a document that indicate where the document should be trimmed.

They are usually located outside the trim area (inside the bleed area) and are used as a guide for cutting the document to its final size. Crop marks are typically placed at the corners of the document and at any other points where the document should be trimmed. They are usually thin lines that are printed in a color that is different from the rest of the document, such as black or blue. When a document is printed with crop marks, it is typically printed on a larger sheet of paper and then trimmed down to its final size using the crop marks as a guide.

CSS bleed and marks (Live Demo)