Opera and Css rendering issue

Question

I have a height rendering issue with Opera. Out of desperation I have been using "em" and this does not provide a workable proportional height rendering (depending on screen size and resolution). In IE and Firefox I am able to use "%". If I use "%" in Opera I get a mess. I am providing the URL because the source itself is too lengthy to post. www.firstport.com

Here is the css that I use for Opera:

 html, body {
 padding: 0px;
   }




 .sectionhead {

 border-style: ridge;
 background: #ebebeb;
 border-right-width: .09em;
 border-left-width: .09em;
 border-bottom-width: .09em;
 border-top-width: .09em;
 border-color: grey;
 float: left;
 overflow:auto;
 width: 99.993%;
 height: 6em;
 text-align: left;
 }

 .sectionhead a {
 color: black;
 background: #EBEBEB;
 font-weight: normal;
 margin-left:2px;
 text-decoration:none;
 }


.SubHeaderLink a {
text-decoration:none;
color: #006633;
background: #EBEBEB;
}

.SubHeaderLink A:hover{ color: blue; background: #EBEBEB; text-decoration:underline; }

.popuplink a { color: blue; background: #EBEBEB; font-weight: normal; margin-left:2px; text-decoration:underline; }