JSFiddle - React, Tailwind, and code Playground

HTML

<div class="content">
<div id="calbox">
<div class="inner">
<table class="cal">
  <tr class="year">
    <th colspan="8">Januar 2012</th>
  </tr>
  <tr class="days">
    <td>Mo</td>
    <td>Di</td>
    <td>Mi</td>
    <td>Do</td>
    <td>Fr</td>
    <td>Sa</td>
    <td>So</td>
    <td>&nbsp;</td>
  </tr>
  <tr>
    <td colspan="6">&nbsp;</td>
    <td title="Neujahr" class="su">1</td>
    <td><input type="checkbox" value="1" name="t201252" checked="checked" id="t201252b" /></td>
  </tr>
  <tr>
    <td>2</td>
    <td>3</td>
    <td>4</td>
    <td>5</td>
    <td>6</td>
    <td class="sa">7</td>
    <td class="su">8</td>
    <td><input type="checkbox" value="1" name="t201201" /></td>
  </tr>
  <tr>
    <td>9</td>
    <td>10</td>
    <td>11</td>
    <td>12</td>
    <td>13</td>
    <td class="sa">14</td>
    <td class="su">15</td>
    <td><input type="checkbox" value="1" name="t201202" /></td>
  </tr>
  <tr>
    <td>16</td>
    <td>17</td>
    <td>18</td>
    <td>19</td>
    <td>20</td>
    <td class="sa">21</td>
    <td class="su">22</td>
    <td><input type="checkbox" value="1" name="t201203" /></td>
  </tr>
  <tr>
    <td>23</td>
    <td>24</td>
    <td>25</td>
    <td>26</td>
    <td>27</td>
    <td class="sa">28</td>
    <td class="su">29</td>
    <td><input type="checkbox" value="1" name="t201204" /></td>
  </tr>
  <tr>
    <td>30</td>
    <td>31</td>
    <td colspan="5">&nbsp;</td>
    <td><label for="t201205b"><input type="checkbox" value="1" name="t201205" checked="checked" id="t201205a" /></label></td>
  </tr>
</table>
<table class="cal">
  <tr class="year">
    <th colspan="8">Februar 2012</th>
  </tr>
  <tr class="days">
    <td>Mo</td>
    <td>Di</td>
    <td>Mi</td>
    <td>Do</td>
    <td>Fr</td>
    <td>Sa</td>
    <td>So</td>
    <td>&nbsp;</td>
  </tr>
  <tr>
    <td colspan="2">&nbsp;</td>
    <td>1</td>
    <td>2</td>
    <td>3</td>
    <td class="sa">4</td>
    <td class="su">5</td>
    <td><label for="t201205a"><input type="checkbox" value="1"...

CSS

.cal {
    border:0;
    font-size:8pt;
    font-family:Verdana;
    height:150px;
    margin-left:2em;
    float:left;
}
.year {
    font-size:12pt;
    font-family:Arial;
    color:#ff9900;
}
.days {
    color:#666;
    font-weight:bold;
}
.cal td {
    text-align:center;
}
.today {
    background-color:red;
    color:white;
}
.sa {
    color:blue;
}
.su {
    color:red;
}
.br {
    font-weight:bold;
}
.cal input {
    margin:auto;
}
.cal th {
    height:1.05em;
}
.content {
    width:960px;
    height:100%;
    margin:0 auto;
}
#calbox {
    background-color:#cff;
    height:150px;
    min-height:150px;
    max-height:80%;
    width:530px;
    min-width:175px;
    max-width:100%;
    overflow-y:auto;
    overflow-x:hidden;
    resize:both;
}
.inner {
    margin-left:-1.2em;
}