Simply removing the specification for the background altogether, will make it 100% transparent.
For example:
/* used on almost every page, is the style of one of the row-types in a table with alternating row types */
.list1,.l1{ font-size: 9pt;
}
/* used on almost every page, is the style of the other of the row-types in a table with alternating row types */
.list2,.l2{ font-size: 9pt;
}
Notice, that they don't have background specifications anymore. That would be sufficient.