I am unable to see a class which is inside another class.
If I remove the </div> above the class and insert it below the text shows but I can't position it.

html code is;
HTML Code:
<div class="txt-6">
<h4> Postcards</h4>
 <p>Donate 51$ - 60$ USA <br/>
  &nbsp;&nbsp;(£34.00 - £40.00, 39,25€ - 46,15€) and</p>
<p><font color="blue">1.</font> Receive this pack of 5 postcards</p>
<p><font color="blue">2.</font>Get an A3 poster with an encouraging verse and<br/>
   <p><font color="blue">3.</font> A Photographic fridge magnet<br/>
      <font color="blue"> 4.</font>  A photographic Keyring<br/>
      <font color="blue"> 5.</font> A Photographic bookmark<br/>
      <font color="blue"> 6.</font> A mention in our newsletter<br/>
      <font color="blue"> 7.</font> A copy of our newsletter </p>  
 <h4>5 postcards pack details;</h4>
       <p>* 5 different designs in a pack <br/> 
       * printed on silk card for richer colours<br/>
       * gloss coating on outside<br/>
       * Size 150 x 100 mm - 6 x 4 inches</p>

</div>                           <--- if I delete this </div> the text shows but can't position it !-->

<div class="post-col">
<h4> Special Service for postcard collectors</h4>
<p> If you are a postcard collector I can send the postcards to you with a personal message and a postage stamp.<br/>
    This requires an additional donation of 6$ USA, £4.00 GBP or 5€ to cover the worldwide postage costs for each <br/>
    card. Please let me know what message you want writing on them and the delivery address.</p>
<a href="#top">Top</a>
The css code is

.postcard {   position: relative;
             height: 45em;
            border: 2px inset;
            margin-top: 20px;
             margin-left: 10%;
            margin-right: 10%;
            background-color: white;
            padding-left: 15px;
            padding-bottom: 15px;
.postcard img { position: relative;
                top: 5px;
                left: 30px;
                max-width: 100%;
                height: auto;
                margin-top: 5px;
                border-style: outset;
                border-width: 2px;
                border-color: #D5D6FF;

.txt-6 {  position:relative;
          top: -230px;
          left: 320px;
          font-family: arial, sans-serif;
          font-size: 1.10em;
          color: black;
          text-align: left;        

/* this section is the problem*/

.post-col { display: block;
           top: -110px;
           left: 10px;
          width: 600px;
          height: 100px;
          font-family: arial, sans-serif;
          font-size: 0.80em;
          color: black;
          text-align: left; 
The site is here