Comment by tambourine_man

Just put the textarea in the left panel.

He asked for the layout in HTML5, not the same code. Separating content from presentation is a better practice than shoveling it all in a table.

   <!doctype html>
   
           <style type="text/css">
               * { -moz-box-sizing: border-box; -webkit-box-sizing: border-box; box-sizing: border-box; }
       
               html, body, form { 
                   height: 100%;
                   width: 100%;
                   border: 0px;
                   margin: 0px;
                   padding: 0px;
               }
   
               .header,.footer { 
                   width: 100%;
                   height: 10%; /*use percentage or fixed size*/
                   border: 1px solid red;
               }
   
               .content {
                   width: 100%;
                   height: 80%;
               }
   
               .leftPanel, .rightPanel {
                   width: 50%;
                   float: left;
                   border: 1px solid red;
                   height: 100%;
               }

               textarea { width: 100%; height: 100% }
   
           </style>
   
           <body>
               <form action="go.php" method="post">
                   <div class="header">Hey I'm a header</div>
                   <div class="content">
                       <div class="leftPanel">
                           <textarea name="text">Write here</textarea>
                       </div>
                       <div class="rightPanel">Right Panel</div>
                   </div>
                   <div class="footer">
                       I'm a footer, hit submit<br>
                       <input type="submit" class="submit" value="submit" name="" />
                   </div>
               </form>
           </body>