.o { color: red }
.i { color: green }
.t { color: blue }
.h { color: black }

table.gantt { border-collapse: collapse; border: solid }
table.gantt tbody {border: solid}
table.gantt colgroup { border-left: solid }
table.gantt td {border: thin solid; border-color: black; text-align: center}
table.gantt th {border: thin solid; border-color: black; text-align: left}
table.gantt tr:nth-child(4n+2) {background: #aaa} /*This code is CSS3*/
table.gantt tr:nth-child(4n+4) {background: #ccc} /*This code is CSS3*/