This CSS replaces all of the images in the table's border with ones that have proper transparency.
<!--<style>
td>img[src*='i_m'], td>img[src*='i_t'] {box-sizing: border-box; padding-top: 19px; height: 19px;}
td>img[src*='i_b'], td>img[src*='i_tb'] {box-sizing: border-box; padding-top: 5px; height: 5px;}
td>img[src*='i_bbar'] {background-image: url(data:image/gif;base64,R0lGODlhAQAFAIABAAAAAP///yH5BAEAAAEALAAAAAABAAUAAAIDTGAFADs=);}
td>img[src*='i_bl'] {background-image: url(data:image/gif;base64,R0lGODlhBQAFAIABAAAAAP///yH5BAEAAAEALAAAAAAFAAUAAAIHTGCGCZ2fCgA7);}
td>img[src*='i_br'] {background-image: url(data:image/gif;base64,R0lGODlhBQAFAIABAAAAAP///yH5BAEAAAEALAAAAAAFAAUAAAIHTGCGB5ufCgA7);}
td[style*='i_m'] {background-image: url(data:image/gif;base64,R0lGODlhBQATAIABAAAAAP///yH5BAEAAAEALAAAAAAFABMAAAIQTGCGuZr3GmSx0uvwzHzPAgA7) !important;}
td>img[src*='i_ml'] {background-image: url(data:image/gif;base64,R0lGODlhBQATAIABAAAAAP///yH5BAEAAAEALAAAAAAFABMAAAIQjI8GuNfKolPgBYslnDylAgA7);}
td>img[src*='i_mr'] {background-image: url(data:image/gif;base64,R0lGODlhBQATAIABAAAAAP///yH5BAEAAAEALAAAAAAFABMAAAIQjI8GuNfKomOgvXCzhKmnAgA7);}
td>img[src*='i_tbar'] {background-image: url(data:image/gif;base64,R0lGODlhAQAFAIABAAAAAP///yH5BAEAAAEALAAAAAABAAUAAAIDTGAFADs=);}
td>img[src*='i_tl'] {background-image: url(data:image/gif;base64,R0lGODlhBQATAIABAAAAAP///yH5BAEAAAEALAAAAAAFABMAAAIPjI+py20AHwKzHnqtzKEAADs=);}
td>img[src*='i_tr'] {background-image: url(data:image/gif;base64,R0lGODlhBQATAIABAAAAAP///yH5BAEAAAEALAAAAAAFABMAAAIOjI+pyw2PQJxHVmpspgUAOw==);}
</style>
-->
There's an alternative that takes advantage of the multiply blend mode since the images' backgrounds are white, but it's also got less browser support.
<!--<style>
td>img[src*='i_b'],td>img[src*='i_m'],td>img[src*='i_t'],td[style*='i_m']{mix-blend-mode:multiply;}
</style>
-->