moodle/grade/report/user/styles.php

.grade-report-user table.user-grade .datesubmitted {
  font-size: 0.7em;
}

.grade-report-user table.user-grade .courseitem,
.grade-report-user table.user-grade .categoryitem {
  font-weight: bold;
}

.grade-report-user table.user-grade td.cell {
  padding-left: 5px;
  padding-right: 5px;
}

#graded_users_selector {
  float: right;
  text-align: right;
}

/* this must be last if we want to override other category and course item colors */
.grade-report-user table.user-grade .hidden,
.grade-report-user table.user-grade .hidden a {
  color:#aaaaaa;
}

table.user-grade {
   border: 1px solid black;
   margin: auto;
   padding: 0.25em;
   font-size: 0.8em;
}
table.user-grade td {
   margin: 1px;
   padding: 0.25em;
}
table.user-grade thead {
   border-bottom: 3px double black;
}
table.user-grade thead th {
   padding: 0.25em 0.75em 0.25em 0.75em;
}

table.user-grade td.oddd1 {
   background-color: #f3dfd0;
}
table.user-grade td.oddd2 {
   background-color: #d0dbf3;
}
table.user-grade td.oddd3 {
   background-color: #d0f3d6;
}
table.user-grade td.oddd4 {
   background-color: #f0f0aa;
}

table.user-grade td.evend2 {
   background-color: #b0bbd3;
}
table.user-grade td.evend3 {
   background-color: #b0dfb6;
}
table.user-grade td.evend4 {
   background-color: #cac8be;
}

table.user-grade td.b1t {
   border-top: 1px solid black;
}
table.user-grade td.b1r {
   border-right: 1px solid black;
}
table.user-grade td.b1b {
   border-bottom: 1px solid black;
}
table.user-grade td.b1l {
   border-left: 1px solid black;
}

table.user-grade td.b2t {
   border-top: 2px solid black;
}
table.user-grade td.b2r {
   border-right: 2px solid black;
}
table.user-grade td.b2b {
   border-bottom: 2px solid black;
}
table.user-grade td.b2l {
   border-left: 2px solid black;
}

table.user-grade td.baggt,
table.user-grade td.baggb {
   font-style: italic;
   font-weight: bold;
}
table.user-grade td.baggt {
   border-top: 3px double black;
}
table.user-grade td.baggb {
   border-bottom: 3px double black;
}

table.user-grade td.item {
   border-left: 1px solid gray;
   border-right: 1px solid gray;
}
table.user-grade td.excluded {
   /*text-decoration: line-through;*/
   background-color: #666;
}
table.user-grade td.hidden {
   color: #aaa;
}

table.user-grade td {
   min-width: 0.5em;
   vertical-align: top;
}