Can someone help me tweaking my web site enbedded CSS for improved backward compatibility and schrinking the code?

Code:
 /* ###### Copyright Webnauts Net###### */
 body{color: #000; background-color: #fff; font-size: 80%; margin: 0em; padding: 0em; background-repeat: no-repeat; background-attachment: scroll; font-family: arial, verdana, helvetica, tahoma, sans-serif}
 h1, h2, h3, h4, h5, h6 {color: #000; background-image: url("http://www.webnauts.net/images/h_gradient.jpg");
 background-repeat: repeat-x; padding-left: 0.6em; padding-right: 0.6em; font-weight: bold; font-size: 1.2em; padding-top: 0.2em; padding-bottom: 0.2em; margin-top: 1.0em}
 a:visited img.square {height: 0.4em; width: 0.4em; vertical-align: 20%; border: none; background: #800080; color: #fff}
 a:hover img.square {height: 0.4em; width: 0.4em; vertical-align: 20%; border: none; background: #800080; color: #fff}
 a:hover img.square1 {height: 0.4em; width: 0.4em; vertical-align: 20%; border: none; background: #fff; color: #000}
 img {border: none; margin-top: 0.55em}
 img.square {height: 0.4em; width: 0.4em; vertical-align: 20%; border: none; background: #000; color: #fff}
 img.right {float: right; margin-left: 0em; padding-right: 0em}
 img.leftone {float: left; margin-top: 0em; margin-left: 3.3em; }
 img.left{float: left; margin-top: 0em; margin-left: 0.7em; padding-right: 1.4em; padding-bottom: 0.45em}
 img.square1 {height: 0.4em; width: 0.4em; vertical-align: 20%; border: none; background: #000; color: #fff}
 p.danke {color: #000; font-size: 1.0em; font-weight: bold; text-align: center; background-color: #fff}
 p.fehler {color: red; font-size: 1.1em; font-weight: bold; text-align: center; background-color: #FBFBFB}
 p.lila {color: #000; font-family: arial, verdana, helvetica, tahoma, sans-serif; font-size: 0.9em; font-weight: bold; font-style: italic; text-align: center; background-color: #fff}
 dt {font-weight: bold; padding-left: 0.6em; padding-right: 0.6em; font-size: 1.1em}
 dd {padding-left: 0.6em; padding-right: 3em; padding-bottom: 0.25em}
 html>body q span {display:none}
 .smallCaps {font-variant: small-caps}
 code {font-family: monospace}
 acronym {border-bottom-style: dotted; border-bottom-width: 0.09em; cursor: help; color: #000; background-color: #eee}
 html>#bodyText {height: 1%; float: left; margin: 0em}
 #bodyText {background-repeat: no-repeat; background-position: center; background-color: #FBFBFB; color: #000; line-height: 1.4em; margin: 0 0 0 15.5em; padding: 1.4em 1.4em 0.9em 1.4em; border-left: 1px solid}
 #bodyText p {padding-left: 0.6em; padding-right: 3em}
 #bodyText a {color: #000; text-decoration: none; border-bottom-style: solid; border-bottom-width: 0.09em}
 #bodyText a:hover {font-weight: bold; border-bottom: none; background-color: #800080; color: #fff; text-decoration: underline}
 #bodyText a:active {border-bottom: none; color: #fff; background-color: #800080; text-decoration: underline}
 #bodyText .topOfPage {font-size: 80%; font-weight: bold; font-variant: small-caps; border: 0; padding: 0.45em 0.6em; float: right; text-decoration: underline}
 #bodyText a.topOfPage:hover {color: #fff; background-color: #800080; text-decoration: none; padding-top: 0.3em; padding-bottom: 0.3em}
 #bodyText li {list-style: square}
 
 #upperMenuBar .highlight, #lowerMenuBar .highlight {color: #000; text-decoration: none}
 #upperMenuBar {height: 2.1em; color: #fff}
 #upperMenuBar a {color: #fff; font-size: 90%; text-decoration: none; padding-left: 0.48em; padding-right: 0.96em}
 #upperMenuBar a:hover {text-decoration: underline; color: #f93}
 .LHS {left: 1.8em; top: 0.8em}
 .RHS a:active {background-color: #eee; color: #000}
 .RHS li {list-style: square; padding: 0; margin-left: 0}
 .RHS ul li a:link {color: #000; background-color: #fff;  text-decoration: none}
 .RHS ul li a:visited {color: #800080; background-color: #fff; text-decoration: none}
 .RHS ul li a:hover {color: #fff; background-color: #800080; text-decoration: none}
 .RHS ul li a:active {color: #000; background-color: #fff; text-decoration: none}
 
 html>body #lowerMenuBar {height:auto;}
 #header {min-height: 75px; padding-left: 0.45em; background-color: #fff; color: #000;}
 * html #header {height:75px}
 * > html #header {height:auto}
 #header .left{margin-left: 1px; margin-top: 10px;width:228px} 
 #lowerMenuBar {clear:both; background-image:url("http://www.webnauts.net/images/nav_gradient.jpg"); background-repeat: repeat-x; color: #000000; font-weight: bold; min-height: 2.9em;line-height:2.9em; padding-left: 0em; padding-right: 1.8em; border-bottom: 1px solid #000; text-align: right}
 * html #lowerMenuBar {height:2em}
 * > html #lowerMenuBar {height:auto}
 .RHS {float:right;margin-right: 1.0em; width: 14.5em; margin-top: 1.0em; font-weight: bold; text-align: left;}
 
 /* Tweaks */
 #header {text-align:center}
 .RHS {float:right;margin-right: .5em; width: 12.5em; margin-top: 1.0em; font-weight: bold; text-align: left;display:inline;}
 img.left{float: left; margin-top: 0em; margin-left: 0.7em; padding-right: .2em; padding-bottom: 0.45em}
 
 #lowerMenuBar a {color: #fff; font-weight: bold; text-decoration: underline; margin: 0 0.5em}
 #lowerMenuBar a:hover {text-decoration: none; color: #000}
 #lowerMenuBar a:visited {color: #800080}
 .sideMenuBox, .sideTextBox {background-color: #eee; color: #000; width: 15.5em; border-bottom: 1px solid; padding: 1.5em 0 1.5em 0em; margin-bottom: 0.05em; float: left; clear: left}
 .sideMenuBox div, .sideTextBox div {font-weight: bold; padding-left: 0.8em; padding-bottom: 0.8em; border-bottom: 0px}
 .sideMenuBox ul li a {list-style: square; text-decoration: none; margin: 1.2em 0 1.2em 0em}
 .sideMenuBox ul {margin-top: 0; margin-left: 2.4em; padding: 0; list-style: none; font-family: arial, verdana, helvetica, tahoma, sans-serif; font-size: 95%; line-height: 150%}
 .sideMenuBox ul li a:hover {text-decoration: underline}
 .sideMenuBox a {color: #000}
 .sideMenuBox a:visited {color: #800080}
 .sideMenuBox a:hover {color: #f93}
 .sideTextBox span {line-height: 1.5em; display: block; padding: 0 0.8em 0 1.06em; list-style: none}
 .sideTextBox a {text-decoration: none; border-bottom-style: solid; border-bottom-width: 0.09em}
 .sideTextBox a:hover {border-bottom: none; text-decoration: underline; background-color: #fff; color: #000}
 .sideTextBox span {color: #000; background-color: #eee}
 .lighterBG {background-color: #fff;color: #000}
 .sideLastBox {font-weight: bold; background-color: #fff; color: #000; width: 15.5em; padding: 1em 0 1em 0; margin-bottom: 0.09em}
 .sideLastBox .centered {margin-left: -1em; border-bottom-style: solid; border-bottom-width: 0.09em}
 div.boxgroup {width: 15.5em; margin: 0 0 0 0; padding: 0; text-align: left; float: left}
 div.centered {text-align: center}
 div.special{text-align: center; margin-right: 2em}
 div.small {font-family: arial, verdana, helvetica, tahoma, sans-serif; font-size: 80%}
 div.row {clear: both; padding-top: 10px; width: 100%; text-align: left}
 div.red {background-color: #fff; color: red; float: right}
 #footer {font-size: 85%; padding: 0em 0.55em 2.4em 0.55em; clear: none; border-top-style: solid;  border-width: 0.00em; background-color: #fff; color: #000}
 #footerlow {background-image:url("http://www.webnauts.net/images/footer_gradient.jpg"); background-repeat: repeat-x; color: #fff; font-size: 30%; padding: 0em 0.55em 1.44em 0.55em; border-top-style: solid; border-width: 0.00em}
 #footer div {text-align: center; line-height: 1.45em; padding-top: 0.1em}
 #footer ul, li {list-style-type: square}
 /*#footer ul, li {list-style-type:none; display: inline; line-height: 1.5em}*/
 #footer a {text-decoration: none; color: blue}
 #footer a:active {background-color: #eee}
 #footer a:hover {background-color: #800080; color: #fff; text-decoration: none}
 .footerLHS {line-height: 1.7em; float: none; clear: none}
 .footerLHSRB {color:#ff0000; line-height: 1.7em; float: none; clear: none}
 fieldset {width: 550px; padding: 10px; border: 1px solid}
 label {color: #000;  background-color: #FBFBFB; font-weight: bold}
 legend {color: #000; background-color: #FBFBFB; font-weight: bold}
 .row label {text-align: right; width: 150px; margin-right: 5px; display: block; float: left}
 .row input {width:200px; text-align: left}
 .row2 input {text-align: right; width: 150px; margin-right: 5px; display: block; float: left}
 .row2 label {width:360px; text-align: left; float: left}
 .row textarea {width:250px; text-align: left} 
 input, textarea {background-color: #eee; border: 1px solid; color: #000;}
 .submit {text-align: center}
Thanks in advance.