CSS 2.1 errors: not a known property name

Here is my code, I got it from an AJAX sample:

body, div, p, h1, h2, h3, h4, ul, li, table
{
    margin:0;
    padding:0;
    border:none;
}

body
{
    background: #B4B4B4 url(images/body_bg.gif) repeat left top;    
    font-family: Tahoma, Arial, sans-serif;
    font-size:75%;
}

/* Master Page Layout */
#master_header
{
    margin: -1px auto 0 auto;
    width: 800px;
}

#master_headertop
{
    background: url(images/headertop_img.jpg) no-repeat left top;
}

#master_headerbottom
{
    background: url(images/headerbottom_img.png) no-repeat left top;
}

#master_page
{
    margin: 5px auto 20px auto;
    width: 800px;
}

#master_menu 
{
    float: left;
    width: 240px;
    padding-right: 10px;
}

.sidebar 
{
    width: 100%;
    margin-bottom: 10px;
}

.sidebarheader
{
    height: 24px;
    padding: 10px 0 0 35px;
    background: url(images/sidebar_header.png) no-repeat left top;
    color: #FFF;
    font-family: Arial, Sans-Serif;
    font-size: 1.2em;
    font-weight: bold;
    text-transform: uppercase;
}

.sidebarcontent
{   
    border: 1px solid #0F2543;
    padding: 20px 20px 20px 30px;
    line-height: 1.5em;
    font-weight: bold;
}

#master_sidebarSamples
{   
    padding-top: 72px;
    background: #FFF url(images/samples_bg.gif) no-repeat left top;
}

#master_sidebarWalkthroughs
{
    padding-top: 72px;
    background: #FFF url(images/walkthrough_bg.gif) no-repeat left top;
}

.sidebarcontent a
{
    padding: 2px 5px;
    color: #5377A9;
    text-decoration: none;
}

.sidebarcontent a:hover
{
    background-color: #0F2543;
    color: #FFF;
}

.sidebarcontent a:visited
{
    font-weight: normal;
}

#master_content
{
    float: left;
    width: 550px;
    margin-right: -550px;
    color: #666666;
}

/*
#master_content a
{
    color: #5377A9;
    padding: 1px;
}

#master_content a:link
{
}

#master_content a:visited
{
}

#master_content a:hover
{
    background-color: #BFBFBF;
    color:#FFF;
}
*/

#master_content ul
{
    margin: 0 25px 0 30px;
}

#master_contentheader
{
    height: 19px;
    background: url(images/rightcoltop.gif) no-repeat right top;
}

#master_contentplaceholder
{
    padding: 30px 20px 40px 20px;
    border-left: 1px solid #0F2543;
    border-right: 1px solid #0F2543;
    border-bottom: 1px solid #0F2543;
    background-color: #EFEFEF;
    line-height: 1.5em;
}

#master_contentfooter
{
    clear: both;
    padding: 10px 0 5px 10px;
    color: #333;
    font-size: 0.8em;
    letter-spacing: 0.1em;
}

/* Content Page Layout             */
.demoarea {
    padding:20px;
    background:#FFF url(images/demotop.png) no-repeat left top;
}

.demoarea p 
{
    padding:5px;
}

.demoheading {
    padding-bottom:20px;
    color:#5377A9;
    font-family:Arial, Sans-Serif;
    font-weight:bold;
    font-size:1.5em;
}

.demobottom {
    height:8px;
    background:#FFF url(images/demobottom.png) no-repeat left bottom;
}


.heading {
    padding: 1em 0 1em 0;
    color:#5377A9;
    font-family:Arial, Sans-Serif;
 开发者_StackOverflow社区   font-weight:bold;
    font-size:1.2em;
}

.subheading{
    padding:.8em 0 0.5em 0;
    color:#0F2543;
    font-weight:bold;
    font-family:Arial, Sans-Serif;
    font-size:1.1em;
}

p {}

em {font-style:italic}

i {font-style: italic;}

strong {font-weight:bold;}

.codeReference
{
    font-family: 'Courier New', Monospace;
    font-style: normal;
    font-weight: bold;
}

pre, code {
    display:block;
    margin:15px 15px 15px 0;
    padding:10px;
    border:1px dashed #CCC;
    background-color:#FFF;
    color:#000;
    font-family:'Courier New', Monospace;
    font-size:0.9em;
    font-style:normal;
}

.releaseList {
    list-style-type:disc;
}


/* Styles for the Animation Reference */
.animationReferenceTable
{
}

.animationReferenceRow
{
}

.animationReferenceField
{
    text-align: right;
    vertical-align: top;
    padding-top: 5px;
}

.animationReferenceCode
{
    margin-top: 5px;
    vertical-align: top;
    font-family: 'Courier New', Monospace;
    font-style: normal;
    font-weight: bold;

    display:block;
    background-color:#FFF;
    color:#000;
    font-family:'Courier New', Monospace;
    font-size:0.9em;
    font-style:normal;
    font-weight: bold;
    margin-bottom: 5px;
}

.animationReferenceItems
{
    vertical-align: top;
}

.animationReferenceItemTable
{
    width: 100%;
    padding: 0px;
    margin: 0px;
}

.animationReferenceItemRow
{
    width: 100%;
    padding: 0px;
    margin: 0px;
}

.animationReferenceItem
{
    width: 100%;
    padding: 0px;
    margin: 0px;
    padding-bottom: 10px;
}

.animationReferenceItemCode
{
    display:block;
    background-color:#FFF;
    color:#000;
    font-family:'Courier New', Monospace;
    font-size:0.9em;
    font-style:normal;
    font-weight: bold;
}

/******************************/
/**Styling information specific to individual content pages**/

/* Accordion */
.accordionHeader
{
    border: 1px solid #2F4F4F;
    color: white;
    background-color: #2E4d7B;
    font-family: Arial, Sans-Serif;
    font-size: 12px;
    font-weight: bold;
    padding: 5px;
    margin-top: 5px;
    cursor: pointer;
}

#master_content .accordionHeader a
{
    color: #FFFFFF;
    background: none;
    text-decoration: none;
}

#master_content .accordionHeader a:hover
{
    background: none;
    text-decoration: underline;
}

.accordionContent
{
    background-color: #D3DEEF;
    border: 1px dashed #2F4F4F;
    border-top: none;
    padding: 5px;
    padding-top: 10px;
}

/*Cascading DropDown*/

/*CollapsiblePanel*/
.collapsePanel {

    background-color:white;
    overflow:hidden;
}

.collapsePanelHeader{   
    width:100%;     
    height:30px;
    background-image: url(images/bg-menu-main.png);
    background-repeat:repeat-x;
    color:#FFF;
    font-weight:bold;
}

#master_content .collapsePanelHeader a {color:#FFF;}
#master_content .collapsePanelHeader a:hover {text-decoration:none;background:none;}

/*Confirm Button*/

/* DropShadow */

#master_content .dropShadowPanel span {color:white;text-decoration:underline;}
#master_content .dropShadowPanel span:hover {text-decoration:none;}


.dropShadowPanel 
{   
    width:300px;    
    background-color:#5377A9;       
    color:white;
    font-weight:bold;       
}

/*Drag Panel*/
.dragMe {
    width:100%;
    height:21px;
    background-color:#FFF;
    background-image:url(images/header-opened.png);
    text-align:center;
    cursor:move;
    font-weight:bold;
}

.overflowHidden {overflow:hidden;}

.overflowScroll {overflow:hidden;}

/*Hover Menu*/
.popupMenu {
    position:absolute;
    visibility:hidden;
    background-color:#F5F7F8;
    opacity:.9;
    filter: alpha(opacity=90);
}

.popupHover {
    background-image:url(images/header-opened.png);
    background-repeat:repeat-x;
    background-position:left top;
    background-color:#F5F7F8;
}

/* PagingBulletedList */
.selectIndex {
    font-weight: bold;
    text-decoration:none;
}
.unselectIndex {
    font-weight:normal;
    text-decoration:underline;
}


/*Modal Popup*/
.modalBackground {
    background-color:Gray;
    filter:alpha(opacity=70);
    opacity:0.7;
}

.modalPopup {
    background-color:#ffffdd;
    border-width:3px;
    border-style:solid;
    border-color:Gray;
    padding:3px;
    width:250px;
}

.sampleStyleA {
    background-color:#FFF;
}

.sampleStyleB {
    background-color:#FFF;
    font-family:monospace;
    font-size:10pt;
    font-weight:bold;
}

.sampleStyleC {
    background-color:#ddffdd;
    font-family:sans-serif;
    font-size:10pt;
    font-style:italic;
}

.sampleStyleD {
    background-color:Blue;
    color:White;
    font-family:Arial;
    font-size:10pt;
}

/*Popup Control*/
.popupControl{
    background-color:White;
    position:absolute;
    visibility:hidden;
}

/*Reorder List*/
.dragHandle {
    width:10px;
    height:15px;
    background-color:Blue;
    background-image:url(images/bg-menu-main.png);
    cursor:move;
    border:outset thin white;
}

.callbackStyle {
    border:thin blue inset;     
}

.callbackStyle table {
    background-color:#5377A9;   
    color:Black;
}


.reorderListDemo li {
    list-style:none;
    margin:2px;
    background-image:url(images/bg_nav.gif);
    background-repeat:repeat-x;
    color:#FFF;
}

.reorderListDemo li a {color:#FFF !important; font-weight:bold;}

.reorderCue {
    border:dashed thin black;
    width:100%;
    height:25px;
}

.itemArea {
    margin-left:15px;
    font-family:Arial, Verdana, sans-serif;
    font-size:1em;
    text-align:left;
}


/* Rounded Corners*/

.roundedPanel
{   
    width:300px;    
    background-color:#5377A9;   
    color:white;
    font-weight:bold;       
}

/* ResizableControl */

.frameImage
{
    width:130px;
    height:65px;
    overflow:hidden;
    float:left;
    padding:3px;
}

.frameText
{
    width:100px;
    height:100px;
    overflow:auto;
    float:left;
    background-color:#ffffff;
    border-style:solid;
    border-width:2px;
    border-color:Gray;
    font-family:Helvetica;
    line-height:normal;
}

.handleImage
{
    width:15px;
    height:16px;
    background-image:url(images/HandleHand.png);
    overflow:hidden;
    cursor:se-resize;
}

.handleText
{
    width:16px;
    height:16px;
    background-image:url(images/HandleGrip.png);
    overflow:hidden;
    cursor:se-resize;
}

.resizingImage
{
    padding:0px;
    border-style:solid;
    border-width:3px;
    border-color:#B4D35D;
}

.resizingText
{
    padding:0px;
    border-style:solid;
    border-width:2px;
    border-color:#7391BA;
}

/*Textbox Watermark*/

.unwatermarked {
    height:18px;
    width:148px;
    font-weight:bold;
}

.watermarked {
    height:20px;
    width:150px;
    padding:2px 0 0 2px;
    border:1px solid #BEBEBE;
    background-color:#F0F8FF;
    color:gray;
}   

/* Rating */
.ratingStar {
    font-size: 0pt;
    width: 13px;
    height: 12px;
    margin: 0px;
    padding: 0px;
    cursor: pointer;
    display: block;
    background-repeat: no-repeat;
}

.filledRatingStar {
    background-image: url(Images/FilledStar.png);

}

.emptyRatingStar {
    background-image: url(Images/EmptyStar.png);
}

.savedRatingStar {
    background-image: url(Images/SavedStar.png);
}


/*Toggle Button*/

/*Setup*/
.walkthrough li {padding-bottom:5px;}

/*Using a sample extender*/

/*Creating a new extender*/
.walkthroughNote {
    padding-left:25px;
    font-style:italic;
}

/*Other neat stuff*/





/************ PasswordStrength Related Styles ***********************/
.TextIndicator_TextBox1
{
     background-color:Gray;
     color:White;
     font-family:Arial;
     font-size:x-small;
     font-style:italic;  
     padding: 2px 3px 2px 3px;   
}

.BarIndicator_TextBox2
{
    color:Blue;
    background-color:Blue;
}

.BarBorder_TextBox2
{
    border-style:solid;
    border-width:1px;
    width:200px;
    vertical-align:middle;
}

.TextIndicator_TextBox3
{
     background-color:Blue;
     color:Yellow;
     font-size:small;
     font-variant:small-caps;  
     padding: 2px 3px 2px 3px;   
}

.TextIndicator_TextBox3_Handle
{
    width:16px;
    height:14px;
    background-image:url(images/Question.png);
    overflow:hidden;
    cursor:help;
}

.dynamicPopulate_Normal 
{   
    border:silver 1px inset;
    padding:2px;
    text-align:center;
    height:2em;
    margin:5px;
    width:200px;
}

.dynamicPopulate_Updating 
{
    background-image:url(images/loading.gif);
    background-repeat:no-repeat;
    border:silver 1px inset;
    text-align:center;
    padding:2px;
    height:2em;
    margin:5px;
    width:200px;
}
/************ MaskedEdit Related Styles ***********************/
.MaskedEditFocus
{
    background-color: #ffffcc;
    color: #000000;
}
.MaskedEditMessage
{
    color: #ff0000;
    font-weight: bold;
}
.MaskedEditError
{
    background-color: #ffcccc;
}
.MaskedEditFocusNegative
{
    background-color: #ffffcc;
    color: #000000;
}
.MaskedEditBlurNegative
{
    color: #ff0000;
}

.MyCalendar .ajax__calendar_container {
    border:1px solid #646464;
    background-color: lemonchiffon;
    color: red;
}
.MyCalendar .ajax__calendar_other .ajax__calendar_day,
.MyCalendar .ajax__calendar_other .ajax__calendar_year {
    color: black;
}
.MyCalendar .ajax__calendar_hover .ajax__calendar_day,
.MyCalendar .ajax__calendar_hover .ajax__calendar_month,
.MyCalendar .ajax__calendar_hover .ajax__calendar_year {
    color: black;
}
.MyCalendar .ajax__calendar_active .ajax__calendar_day,
.MyCalendar .ajax__calendar_active .ajax__calendar_month,
.MyCalendar .ajax__calendar_active .ajax__calendar_year {
    color: black;
    font-weight:bold;
}

.validatorCalloutHighlight 
{
    background-color: lemonchiffon; 
}

I am getting the following errors:

Error 1 Validation (CSS 2.1): 'opacity' is not a known CSS property name. C:\Documents and Settings\agordon\My Documents\Visual Studio 2008\WebSites\WebSite3\StyleSheet.css 402 2 C:...\WebSite3\ Error 2 Validation (CSS 2.1): 'filter' is not a known CSS property name. C:\Documents and Settings\agordon\My Documents\Visual Studio 2008\WebSites\WebSite3\StyleSheet.css 403 2 C:...\WebSite3\ Error 3 Validation (CSS 2.1): 'filter' is not a known CSS property name. C:\Documents and Settings\agordon\My Documents\Visual Studio 2008\WebSites\WebSite3\StyleSheet.css 427 2 C:...\WebSite3\ Error 4 Validation (CSS 2.1): 'opacity' is not a known CSS property name. C:\Documents and Settings\agordon\My Documents\Visual Studio 2008\WebSites\WebSite3\StyleSheet.css 428 2 C:...\WebSite3\ Error 5 Validation (CSS 2.1): 'lemonchiffon' is not a valid value for the 'background-color' property. C:\Documents and Settings\agordon\My Documents\Visual Studio 2008\WebSites\WebSite3\StyleSheet.css 738 23 C:...\WebSite3\ Error 6 Validation (CSS 2.1): 'lemonchiffon' is not a valid value for the 'background-color' property. C:\Documents and Settings\agordon\My Documents\Visual Studio 2008\WebSites\WebSite3\StyleSheet.css 759 23 C:...\WebSite3\

Does anyone know what I am doing wrong?

Validation errors are all fine, because they are using the proper CSS 2.1 Documentation and your trying to validate CSS3 properties in a CSS 2.1 context.

What you probably want is to build your application bypassing the CSS Errors, no matter what they are, for that you can transform this "errors" into warnings using Visual Studio Options:

in The Visual Studio menu click on:

Tools > Options... and drill down Text Editor > CSS > Miscellaneous

and just make the CSS Errors to be treated as warnings

2013 version

You're validating your stylesheets against CSS 2.1, but those properties are CSS3.

Change your stylesheet validation to CSS3.

The errors you are getting are validation errors. Opacity and filter are not in the CSS 2.1 spec despite being supported by all major browsers.

I realize that this response is a little late, but someone else may find this information useful.

To make the filter tag warning go away in VS2010 (as opposed to just ignoring it), close VS2010 and edit the following file: C:\Program Files (x86)\Microsoft Visual Studio 10.0\Common7\Packages\1033\schemas\CSS\css30.xml

You need to change the filter property from enum to composite.

Around line 387, you should find the following text: <cssmd:property-def _locID="filter" _locAttrData="description,syntax" type="enum" ...

Change it to: <cssmd:property-def _locID="filter" _locAttrData="description,syntax" type="composite" ...

Then restart VS2010.

You need to validate this as CSS3

http://jigsaw.w3.org/css-validator/#validate_by_input+with_options

When you do that, you will two errors for your opacity styles and a bunch of warnings dealing with duplicated background-colors.