What you have entered is HTML, you need to construct a CSS Selector and rule - ok, lets say you want to change the color of the month/year on the calander. your generated code is this
HTML Code:
<div id="calendar-3" class="widget widget_calendar">
<div class="widget-title">
<h3> </h3>
</div>
<div id="calendar_wrap">
<table id="wp-calendar" summary="Calendar">
<caption>October 2009</caption>
<thead>
<tr>
<th abbr="Monday" scope="col" title="Monday">M</th>
<th abbr="Tuesday" scope="col" title="Tuesday">T</th>
<th abbr="Wednesday" scope="col" title="Wednesday">W</th>
<th abbr="Thursday" scope="col" title="Thursday">T</th>
<th abbr="Friday" scope="col" title="Friday">F</th>
<th abbr="Saturday" scope="col" title="Saturday">S</th>
<th abbr="Sunday" scope="col" title="Sunday">S</th>
</tr>
</thead>
<tfoot>
<tr>
<td colspan="3" id="prev" class="pad"> </td>
<td class="pad"> </td>
<td colspan="3" id="next" class="pad"> </td>
</tr>
</tfoot>
<tbody>
<tr>
<td colspan="3" class="pad"> </td><td>1</td><td>2</td><td>3</td><td>4</td>
</tr>
<tr>
<td>5</td><td>6</td><td>7</td><td>8</td><td><a href="http://fastyacht.net/wordpress/2009/10/09" title="Fastest yacht in the World">9</a></td><td>10</td><td>11</td>
</tr>
<tr>
<td>12</td><td>13</td><td>14</td><td>15</td><td>16</td><td>17</td><td>18</td>
</tr>
<tr>
<td>19</td><td>20</td><td>21</td><td>22</td><td>23</td><td>24</td><td>25</td>
</tr>
<tr>
<td>26</td><td>27</td><td id="today">28</td><td>29</td><td>30</td><td>31</td>
<td class="pad" colspan="1"> </td>
</tr>
</tbody>
</table></div></div>
You can see that 'October 2009 is in a <caption> but it doesn't have an ID (ID can only be used once in a document) we look at the block in is inside. It's inside a <table> and the table has an ID so you can be very specific here and code
table#wp-calendar caption { <-- this is your css selector - it selects where this CSS will be applied
color: #00FFFF; <-- this is the rule to apply, set the color red'ish
} <-- indicates you are done
so the whole thing would be
HTML Code:
table#wp-calendar caption {
color: #00FFFF;
}