a[rel='attachment'] { 
   display: inline-block;
   padding: 2px 0 2px 18px;
   background: transparent url(../images/icons/file.png) no-repeat center left; 
}

a[rel='attachment'][href$='.pdf'] {
   background-image: url(../images/icons/pdf.png);
}

a[rel='attachment'][href$='.doc'], a[rel='attachment'][href$='.docx'] {
   background-image: url(../images/icons/doc.png);
}

a[rel='attachment'][href$='.xls'], a[rel='attachment'][href$='.xlsx'] {
   background-image: url(../images/icons/xls.png);
}

a[rel='attachment'][href$='.rar'], a[rel='attachment'][href$='.zip'] {
   background-image: url(../images/icons/zip.png);
}