I'd guess that's because of the margin, the margin goes
outside the border, for spacing inside the border you'd have to use padding. Try:
Code:
@page {
size: 85mm 114mm;
margin: 0 1mm 0 1mm !important;
border-width: 0.1px;
border-color:rgb(240,240,240);
padding-top: 2mm;
border-top-style:solid;
padding-bottom: 2mm;
border-bottom-style:solid;
}