calendar-skin.css

/*
YUI 3.5.1 (build 22)
Copyright 2012 Yahoo! Inc. All rights reserved.
Licensed under the BSD License.
http://yuilibrary.com/license/
*/
.yui3-skin-night .yui3-calendar-day-highlighted {
    background-color: #555555;
}

.yui3-skin-night .yui3-calendar-day-selected.yui3-calendar-day-highlighted {
    background-color: #777777;
}