Timespans removing all lines

I am using the following css to mark certain time blocks using zone. These are being applied properly, however, once applied, the lines dividing the hours disappear (please see the attached image). I added the following but the colors get dull and lines appear slightly.
opacity: 0.25;
filter: alpha(opacity=25);

What else I need to set here?

.schedule_block {
background-color: #FFF3A1 !important;
color: #000000 !important;

.schedule_working {
    background-color: #ffffff !important;
    color: #000000 !important;

Marked timespans are rendered in a higher layer than a background of a calendar.
If you don’t specify any opacity in for timespan element, it will completely cover affected area of the calendar.
So you can either set the opacity or set some background image for marked timespan