After feedback from Keyrocks that by using this css file everything works. I relase it for all you who want the styling to match the xhtml doctype. If you have problems try to look me up. This is the default.css file... placed under css in the phpEventCalendar folder.
<STYLE TYPE="text/css">
<!--
/**************************************************************
********* Formatting For Month Table and Text *****************
**************************************************************/
A { font-family:arial, helvetica; color:#00F; text-decoration:underline }
SPAN { font-family:arial, helvetica }
TD { font-family:arial, helvetica }
BODY { background-color:#FFF }
/**** month and year header at top of calendar ****/
.date_header { font-size:16px; font-family:arial, helvetica; font-weight:bold }
/**** color and size of calendar cells. ****/
.day_cell { background-color:#444444; height:80px; width: 95px; }
.empty_day_cell { background-color:#555555; height:80px; width: 95px; }
.today_cell { background-color:#777777; height:80px; width: 95px; }
/**** day number in upper left corner of each cell ****/
.day_number { font-size:10px; font-family:verdana, arial, helvetica; color:#eee }
/**** title_txt is the text for each post on main page ****/
.title_txt { font-size:10px; font-family:verdana, arial, helvetica; color:#eee }
.title_txt A:hover { color:#aaaaaa; text-decoration:underline }
/**** time line under title text when event time given ****/
.time_str { font-size:9px; font-family:arial, helvetica }
/**** column headers or days of the week ****/
.column_header { background-color:#111; font-size:12px; font-family:arial, helvetica; color:#FFFFFF; font-weight:bold;}
/**** footprint text ****/
.footprint { font-size:10px; font-family:verdana, arial, helvetica; color:#000; font-weight:bold; }
.footprint A { font-size:10px; font-family:verdana, arial, helvetica; color:#00F; font-weight:bold; }
// end hiding -->
</STYLE>