DIVs que tomen el tamaño de la pagina web

[emont]

Hola, tengo un codigo css y me gustaría que me ayudaran en donde le puedo colocar la opcion para que me quede siempre ajustada al tamaño del navegador?

este es mi código:

Código HTML:

body  {
    font: 100% Verdana, Arial, Helvetica, sans-serif;
    background: #666666;
    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;
    /*height: 768px;*/
}
.twoColFixLtHdr #container { 
    width: auto; /*780px;*/  /* using 20px less than a full 800px width allows for browser chrome and avoids a horizontal scroll bar */
    background: #FFFFFF;
    margin: 0 auto; /* the auto margins (in conjunction with a width) center the page */
    border: 1px solid #000000;
    text-align: left; /* this overrides the text-align: center on the body element. */
    /*height: 680px;*/
} 
.twoColFixLtHdr #header { 
    background: #048dc6; 
    /*padding: 0 0px 0 0px;*/  /* this padding matches the left alignment of the elements in the divs that appear beneath it. If an image is used in the #header instead of text, you may want to remove the padding. */
} 
.twoColFixLtHdr #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: 0px 0 0px 0; /* using padding instead of margin will allow you to keep the element away from the edges of the div */
}
.twoColFixLtHdr #sidebar1 {
    float: left; /* since this element is floated, a width must be given */
    width: 200px; /* the actual width of this div, in standards-compliant browsers, or standards mode in Internet Explorer will include the padding and border in addition to the width */
    background: #EBEBEB; /* the background color will be displayed for the length of the content in the column, but no further */
    padding: 50px 10px 102px 20px;
}
.twoColFixLtHdr #mainContent { 
    margin: 0 0 0 250px; /* the left margin on this div element creates the column down the left side of the page - no matter how much content the sidebar1 div contains, the column space will remain. You can remove this margin if you want the #mainContent div's text to fill the #sidebar1 space when the content in #sidebar1 ends. */
    padding: 0 20px; /* remember that padding is the space inside the div box and margin is the space outside the div box */
} 
.twoColFixLtHdr #footer { 
    padding: 0 10px 0 20px; /* this padding matches the left alignment of the elements in the divs that appear above it. */
    background:#DDDDDD; 
} 
.twoColFixLtHdr #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: 1px;
    line-height: 0px;
}