Template:Navbox/styles.css

table.navbox {
    border: 1px solid #aaa; 
    width: 100%; 
    margin: auto; 
    clear: both; 
    font-size: 88%; 
    text-align: center; 
    padding: 1px; 
}

table.navbox + table.navbox {
    margin-top: -1px;
}

.navbox-title,
.navbox-abovebelow,
table.navbox th {
    text-align: center;
    padding-left: 1em;
    padding-right: 1em;
}

.navbox-group {
    white-space: nowrap;
    text-align: right;
    font-weight: bold;
    padding-left: 1em;
    padding-right: 1em;
}

.navbox,
.navbox-subgroup {
    background: #fdfdfd;
}

.navbox-list {
    border-color: #fdfdfd;
}

.navbox-title,
table.navbox th {
    background: #ccccff; /* This is the purple/blue background you mentioned */ 
}

.navbox-abovebelow,
.navbox-group,
.navbox-subgroup .navbox-title {
    background: #ddddff;
}

.navbox-subgroup .navbox-group,
.navbox-subgroup .navbox-abovebelow {
    background: #e6e6ff;
}

.navbox-even {
    background: #f7f7f7;
}

.navbox-odd {
    background: transparent;
}

.navbox .collapseButton {
    width: 6em;
}