Help! Divs extend beyond parent container! Clearing doesn't seem to work!

Question

My "mainContent" div extends beyond the "Container" div. It seems that I've tried everything--clearing doesn't seem to work.
Help!
Here is my css:
@charset "UTF-8";
/* CSS Document */
body  {
     margin: 0; /* it's good practice to zero the margin and padding of the body element to account for differing browser defaults */
     padding: 0;
     text-align: center; /* this centers the container in IE 5* browsers. The text is then set to the left aligned default in the #container selector */
     color: #000000;
     font-family: Arial, Helvetica, sans-serif;
     font-size: 100%;
     background-color: #FFF;
.twoColFixRtHdr #container {
     width: 960px;  /* using 20px less than a full 800px width allows for browser chrome and avoids a horizontal scroll bar */
     background: #FFFFFF;
     text-align: left; /* this overrides the text-align: center on the body element. */
     font-family: Arial, Helvetica, sans-serif;
     margin-top: 0;
     margin-right: auto;
     margin-bottom: 0;
     margin-left: auto;
     top: 10px;
     padding-top: 10px;
     clear: both;
.twoColFixRtHdr #header {
     height: 180px;
     padding-top: 10px;
     padding-right: 0px;
     padding-bottom: 5px;
     padding-left: 0px;
     border-top-width: 1px;
     border-right-width: 0px;
     border-bottom-width: 5px;
     border-left-width: 0px;
     border-top-style: solid;
     border-bottom-style: solid;
     border-top-color: #999;
     border-bottom-color: #000;
     margin-top: 5px;
     margin-bottom: 0px;
.twoColFixRtHdr #container #sidebar1 img {
     padding-top: 10px;
     border-bottom-width: 1px;
     border-bottom-style: solid;
     border-bottom-color: #999;
     margin-bottom: 0px;
     padding-bottom: 10px;
     padding-left: 10px;
.twoColFixRtHdr #header h1 {
     margin: 0; /* zeroing the margin of the last element in the #header div will avoid margin collapse - an unexplainable space between divs. If the div has a border around it, this is not necessary as that also avoids the margin collapse */
     padding: 10px 0; /* using padding instead of margin will allow you to keep the element away from the edges of the div */
.twoColFixRtHdr #sidebar1 {
     width: 315px;
     padding: 0px;
     top: 200px;
     float: right;
.twoColFixRtHdr #mainContent {
     width: 643px;
     padding-top: 10px;
     border-right-width: 1px;
     border-right-style: solid;
     border-right-color: #999;
     overflow: hidden;
     top: 230px;
     position: absolute;
     clear: right;
.twoColFixRtHdr #footer {
     background:#DDDDDD;
     top: 50px;
     clear: both;
     padding-top: 0;
     padding-right: 10px;
     padding-bottom: 0;
     padding-left: 20px;
.twoColFixRtHdr #footer p {
     margin: 0; /* zeroing the margins of the first element in the footer will avoid the possibility of margin collapse - a space between divs */
     padding: 10px 0; /* padding on this element will create space, just as the the margin would have, without the margin collapse issue */
.fltrt { /* this class can be used to float an element right in your page. The floated element must precede the element it should be next to on the page. */
     float: right;
     margin-left: 8px;
.fltlft { /* this class can be used to float an element left in your page */
     float: left;
     margin-right: 8px;
.clearfloat { /* this class should be placed on a div or break element and should be the final element before the close of a container that should fully contain a float */
     clear:both;
     height:0;
     font-size: 0px;
     line-height: 0px;
.spacer { 
     clear: both; 
.twoColFixRtHdr #container #mainContent #article_main_head {
     font-family: Arial, Helvetica, sans-serif;
     top: 10px;
     width: 635px;
     float: left;
.twoColFixRtHdr #container #mainContent #article_img {
     width: 630px;
     float: left;
     margin-top: 10px;
     clear: both;
.twoColFixRtHdr #container #mainContent #article_main_txt {
     float: right;
     width: 450px;
     clear: both;
     padding-top: 10px;
     height: 500px;
.twoColFixRtHdr #container #mainContent #article_main_pq {
     clear: both;
     float: left;
     width: 180px;
     margin-top: 100px;
Here is my html:
                                                               Donec eu mi sed turpis feugiat feugiat. Integer turpis arcu, pellentesque  eget, cursus et, fermentum ut, sapien. Fusce metus mi, eleifend  sollicitudin, molestie id, varius et, nibh. Donec nec libero. 
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Answer 1

This CSS sends up a red flag:
.twoColFixRtHdr #mainContent {
     width: 643px;
     padding-top: 10px;
     border-right-width: 1px;
     border-right-style: solid;
     border-right-color: #999;
     overflow: hidden;
/******DELETE THE FOLLOWING*****/
     top: 230px;
     position: absolute;
     clear: right;
Nancy O.
Alt-Web Design & Publishing
Web | Graphics | Print | Media  Specialists
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