如何让IE 低版本下支持 css3属性

依赖源  该文件为  ie-css3.htc    （特别提示.htc为二进制文件，只会在ie中识别,让IE浏览器支持CSS3的一些属性）

以下为依赖文件源码

　　通过源码我们可以看到 该文件在一定程度上类似于我们所使用的javascrip

--Do not remove this if you are using--
Original Author: Remiz Rahnas
Original Author URL: http://www.htmlremix.com
Published date: 2008/09/24

Changes by Nick Fetchak:
- IE8 standards mode compatibility
- VML elements now positioned behind original box rather than inside of it - should be less prone to breakage
- Added partial support for 'box-shadow' style
- Checks for VML support before doing anything
- Updates VML element size and position via timer and also via window resize event
- lots of other small things
Published date : 2010/03/14
http://fetchak.com/ie-css3

Thanks to TheBrightLines.com (http://www.thebrightlines.com/2009/12/03/using-ies-filter-in-a-cross-browser-way) for enlightening me about the DropShadow filter

<public:attach event="ondocumentready" onevent="ondocumentready('v08vnSVo78t4JfjH')" />
<script type="text/javascript">

timer_length = 200; // Milliseconds
border_opacity = false; // Use opacity on borders of rounded-corner elements? Note: This causes antialiasing issues

// supportsVml() borrowed from http://*.com/questions/654112/how-do-you-detect-support-for-vml-or-svg-in-a-browser
function supportsVml() {
    if (typeof supportsVml.supported == "undefined") {
        var a = document.body.appendChild(document.createElement('div'));
        a.innerHTML = '<v:shape id="vml_flag1" adj="1" />';
        var b = a.firstChild;
        b.style.behavior = "url(#default#VML)";
        supportsVml.supported = b ? typeof b.adj == "object": true;
        a.parentNode.removeChild(a);
    }
    return supportsVml.supported
}

// findPos() borrowed from http://www.quirksmode.org/js/findpos.html
function findPos(obj) {
    var curleft = curtop = 0;

    if (obj.offsetParent) {
        do {
            curleft += obj.offsetLeft;
            curtop += obj.offsetTop;
        } while (obj = obj.offsetParent);
    }

    return({
        'x': curleft,
        'y': curtop
    });
}

function createBoxShadow(element, vml_parent) {
    var style = element.currentStyle['iecss3-box-shadow'] || element.currentStyle['-moz-box-shadow'] || element.currentStyle['-webkit-box-shadow'] || element.currentStyle['box-shadow'] || '';
    var match = style.match(/^(\d+)px (\d+)px (\d+)px/);
    if (!match) { return(false); }

    var shadow = document.createElement('v:roundrect');
    shadow.userAttrs = {
        'x': parseInt(RegExp.$1 || 0),
        'y': parseInt(RegExp.$2 || 0),
        'radius': parseInt(RegExp.$3 || 0) / 2
    };
    shadow.position_offset = {
        'y': (0 - vml_parent.pos_ieCSS3.y - shadow.userAttrs.radius + shadow.userAttrs.y),
        'x': (0 - vml_parent.pos_ieCSS3.x - shadow.userAttrs.radius + shadow.userAttrs.x)
    };
    shadow.size_offset = {
        'width': 0,
        'height': 0
    };
    shadow.arcsize = element.arcSize +'px';
    shadow.style.display = 'block';
    shadow.style.position = 'absolute';
    shadow.style.top = (element.pos_ieCSS3.y + shadow.position_offset.y) +'px';
    shadow.style.left = (element.pos_ieCSS3.x + shadow.position_offset.x) +'px';
    shadow.style.width = element.offsetWidth +'px';
    shadow.style.height = element.offsetHeight +'px';
    shadow.style.antialias = true;
    shadow.className = 'vml_box_shadow';
    shadow.style.zIndex = element.zIndex - 1;
    shadow.style.filter = 'progid:DXImageTransform.Microsoft.Blur(pixelRadius='+ shadow.userAttrs.radius +',makeShadow=true,shadowOpacity='+ element.opacity +')';

    element.parentNode.appendChild(shadow);
    //element.parentNode.insertBefore(shadow, element.element);

    // For window resizing
    element.vml.push(shadow);

    return(true);
}

function createBorderRect(element, vml_parent) {
    if (isNaN(element.borderRadius)) { return(false); }

    element.style.background = 'transparent';
    element.style.borderColor = 'transparent';

    var rect = document.createElement('v:roundrect');
    rect.position_offset = {
        'y': (0.5 * element.strokeWeight) - vml_parent.pos_ieCSS3.y,
        'x': (0.5 * element.strokeWeight) - vml_parent.pos_ieCSS3.x
    };
    rect.size_offset = {
        'width': 0 - element.strokeWeight,
        'height': 0 - element.strokeWeight
    };
    rect.arcsize = element.arcSize +'px';
    rect.strokeColor = element.strokeColor;
    rect.strokeWeight = element.strokeWeight +'px';
    rect.stroked = element.stroked;
    rect.className = 'vml_border_radius';
    rect.style.display = 'block';
    rect.style.position = 'absolute';
    rect.style.top = (element.pos_ieCSS3.y + rect.position_offset.y) +'px';
    rect.style.left = (element.pos_ieCSS3.x + rect.position_offset.x) +'px';
    rect.style.width = (element.offsetWidth + rect.size_offset.width) +'px';
    rect.style.height = (element.offsetHeight + rect.size_offset.height) +'px';
    rect.style.antialias = true;
    rect.style.zIndex = element.zIndex - 1;

    if (border_opacity && (element.opacity < 1)) {
        rect.style.filter = 'progid:DXImageTransform.Microsoft.Alpha(Opacity='+ parseFloat(element.opacity * 100) +')';
    }

    var fill = document.createElement('v:fill');
    fill.color = element.fillColor;
    fill.src = element.fillSrc;
    fill.className = 'vml_border_radius_fill';
    fill.type = 'tile';
    fill.opacity = element.opacity;

    // Hack: IE6 doesn't support transparent borders, use padding to offset original element
    isIE6 = /msie|MSIE 6/.test(navigator.userAgent);
    if (isIE6 && (element.strokeWeight > 0)) {
        element.style.borderStyle = 'none';
        element.style.paddingTop = parseInt(element.currentStyle.paddingTop || 0) + element.strokeWeight;
        element.style.paddingBottom = parseInt(element.currentStyle.paddingBottom || 0) + element.strokeWeight;
    }

    rect.appendChild(fill);
    element.parentNode.appendChild(rect);
    //element.parentNode.insertBefore(rect, element.element);

    // For window resizing
    element.vml.push(rect);

    return(true);
}

function createTextShadow(element, vml_parent) {
    if (!element.textShadow) { return(false); }

    var match = element.textShadow.match(/^(\d+)px (\d+)px (\d+)px (#?\w+)/);
    if (!match) { return(false); }

    //var shadow = document.createElement('span');
    var shadow = element.cloneNode(true);
    var radius = parseInt(RegExp.$3 || 0);
    shadow.userAttrs = {
        'x': parseInt(RegExp.$1 || 0) - (radius),
        'y': parseInt(RegExp.$2 || 0) - (radius),
        'radius': radius / 2,
        'color': (RegExp.$4 || '#000')
    };
    shadow.position_offset = {
        'y': (0 - vml_parent.pos_ieCSS3.y + shadow.userAttrs.y),
        'x': (0 - vml_parent.pos_ieCSS3.x + shadow.userAttrs.x)
    };
    shadow.size_offset = {
        'width': 0,
        'height': 0
    };
    shadow.style.color = shadow.userAttrs.color;
    shadow.style.position = 'absolute';
    shadow.style.top = (element.pos_ieCSS3.y + shadow.position_offset.y) +'px';
    shadow.style.left = (element.pos_ieCSS3.x + shadow.position_offset.x) +'px';
    shadow.style.antialias = true;
    shadow.style.behavior = null;
    shadow.className = 'ieCSS3_text_shadow';
    shadow.innerHTML = element.innerHTML;
    // For some reason it only looks right with opacity at 75%
    shadow.style.filter = '\
        progid:DXImageTransform.Microsoft.Alpha(Opacity=75)\
        progid:DXImageTransform.Microsoft.Blur(pixelRadius='+ shadow.userAttrs.radius +',makeShadow=false,shadowOpacity=100)\
    ';

    var clone = element.cloneNode(true);
    clone.position_offset = {
        'y': (0 - vml_parent.pos_ieCSS3.y),
        'x': (0 - vml_parent.pos_ieCSS3.x)
    };
    clone.size_offset = {
        'width': 0,
        'height': 0
    };
    clone.style.behavior = null;
    clone.style.position = 'absolute';
    clone.style.top = (element.pos_ieCSS3.y + clone.position_offset.y) +'px';
    clone.style.left = (element.pos_ieCSS3.x + clone.position_offset.x) +'px';
    clone.className = 'ieCSS3_text_shadow';

    element.parentNode.appendChild(shadow);
    element.parentNode.appendChild(clone);

    element.style.visibility = 'hidden';

    // For window resizing
    element.vml.push(clone);
    element.vml.push(shadow);

    return(true);
}

function ondocumentready(classID) {
    if (!supportsVml()) { return(false); }

  if (this.className.match(classID)) { return(false); }
    this.className = this.className.concat(' ', classID);

    // Add a namespace for VML (IE8 requires it)
    if (!document.namespaces.v) { document.namespaces.add("v", "urn:schemas-microsoft-com:vml"); }

    // Check to see if we've run once before on this page
    if (typeof(window.ieCSS3) == 'undefined') {
        // Create global ieCSS3 object
        window.ieCSS3 = {
            'vmlified_elements': new Array(),
            'update_timer': setInterval(updatePositionAndSize, timer_length)
        };

        if (typeof(window.onresize) == 'function') { window.ieCSS3.previous_onresize = window.onresize; }

        // Attach window resize event
        window.onresize = updatePositionAndSize;
    }

    // These attrs are for the script and have no meaning to the browser:
    this.borderRadius = parseInt(this.currentStyle['iecss3-border-radius'] ||
                                 this.currentStyle['-moz-border-radius'] ||
                                 this.currentStyle['-webkit-border-radius'] ||
                                 this.currentStyle['border-radius'] ||
                                 this.currentStyle['-khtml-border-radius']);
    this.arcSize = Math.min(this.borderRadius / Math.min(this.offsetWidth, this.offsetHeight), 1);
    this.fillColor = this.currentStyle.backgroundColor;
    this.fillSrc = this.currentStyle.backgroundImage.replace(/^url\("(.+)"\)$/, '$1');
    this.strokeColor = this.currentStyle.borderColor;
    this.strokeWeight = parseInt(this.currentStyle.borderWidth);
    this.stroked = 'true';
    if (isNaN(this.strokeWeight) || (this.strokeWeight == 0)) {
        this.strokeWeight = 0;
        this.strokeColor = fillColor;
        this.stroked = 'false';
    }
    this.opacity = parseFloat(this.currentStyle.opacity || 1);
    this.textShadow = this.currentStyle['text-shadow'];

    this.element.vml = new Array();
    this.zIndex = parseInt(this.currentStyle.zIndex);
    if (isNaN(this.zIndex)) { this.zIndex = 0; }

    // Find which element provides position:relative for the target element (default to BODY)
    vml_parent = this;
    var limit = 100, i = 0;
    do {
        vml_parent = vml_parent.parentElement;
        i++;
        if (i >= limit) { return(false); }
    } while ((typeof(vml_parent) != 'undefined') && (vml_parent.currentStyle.position != 'relative') && (vml_parent.tagName != 'BODY'));

    vml_parent.pos_ieCSS3 = findPos(vml_parent);
    this.pos_ieCSS3 = findPos(this);

    var rv1 = createBoxShadow(this, vml_parent);
    var rv2 = createBorderRect(this, vml_parent);
    var rv3 = createTextShadow(this, vml_parent);
    if (rv1 || rv2 || rv3) { window.ieCSS3.vmlified_elements.push(this.element); }

    if (typeof(vml_parent.document.ieCSS3_stylesheet) == 'undefined') {
        vml_parent.document.ieCSS3_stylesheet = vml_parent.document.createStyleSheet();
        vml_parent.document.ieCSS3_stylesheet.addRule("v\\:roundrect", "behavior: url(#default#VML)");
        vml_parent.document.ieCSS3_stylesheet.addRule("v\\:fill", "behavior: url(#default#VML)");
        // Compatibility with IE7.js
        vml_parent.document.ieCSS3_stylesheet.ie7 = true;
    }
}

function updatePositionAndSize() {
    if (typeof(window.ieCSS3.vmlified_elements) != 'object') { return(false); }

    for (var i in window.ieCSS3.vmlified_elements) {
        var el = window.ieCSS3.vmlified_elements[i];

        if (typeof(el.vml) != 'object') { continue; }

        for (var z in el.vml) {
            //var parent_pos = findPos(el.vml[z].parentNode);
            var new_pos = findPos(el);
            new_pos.x = (new_pos.x + el.vml[z].position_offset.x) + 'px';
            new_pos.y = (new_pos.y + el.vml[z].position_offset.y) + 'px';
            if (el.vml[z].style.left != new_pos.x) { el.vml[z].style.left = new_pos.x; }
            if (el.vml[z].style.top != new_pos.y) { el.vml[z].style.top = new_pos.y; }

            var new_size = {
                'width': parseInt(el.offsetWidth + el.vml[z].size_offset.width),
                'height': parseInt(el.offsetHeight + el.vml[z].size_offset.height)
            }
            if (el.vml[z].offsetWidth != new_size.width) { el.vml[z].style.width = new_size.width +'px'; }
            if (el.vml[z].offsetHeight != new_size.height) { el.vml[z].style.height = new_size.height +'px'; }
        }
    }

    if (event && (event.type == 'resize') && typeof(window.ieCSS3.previous_onresize) == 'function') { window.ieCSS3.previous_onresize(); }
}
</script>

示例代码：

俗话说的好书面描述的再好，都不如上手来段代码实践一波来的实际，当然该代码均为在本地环境下的实践，在低版本ie下的css3效果当然也不如符合W3C的正统css3展示的美观

　　毕竟不是浏览器自带的属性，使用时遇到问题在所难免，这里说一下一些注意事项，也可以说是方法的局限性吧：

1. 当前元素一定要有定位属性，像是position:relative或是position:absolute属性。
2. z-index值一定要比周围元素的要高，否则……只能说抱歉了~~
3. http协议访问。
4. 原生IE浏览器访问，兼容模式显示可能没效果。

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>低版本ie-支持css3</title>
    <style>
        body {
            background: #fff;
        }

        .box {
            background: #f8f8f8;
            /* 通知IE浏览器调用脚本作用于'box'类 */
            behavior: url(htc-css3.htc);
            /* 现代浏览器以及使用了IE-CSS3的IE浏览器 */
            border-radius: 15px;
            /* 现代浏览器以及使用了IE-CSS3的IE浏览器 */
            box-shadow: 2px 2px 8px #000;
            display: inline-block;
            padding: 10px;
            height: 60px;
        }

    </style>
</head>

<body>
    <div class="box">
        看到一本书里的一句话，大意是:“如果你满脑子都是一个人，你会发现你们之间有很多巧合，所有那些被你认为是心有灵犀的事件都只是你太刻意的关注罢了”。
        <br>
        有人说:“遇见爱，遇见性，都不算难，难得是遇见了解，爱可以是一见钟情，性只需要几分钟，而了解可能需要一辈子。”
        <br>
        知道我看到一本书觉得在精神上无比的契合，我记得原话是“一段好的爱情，不是互相占有，而是共同成长。”
    </div>
</body>

</html>

通过源码我们可以清晰的看到这份htc文件所支持的css属性（如下表）【当然我们也可以自己通过对源码的拓展来创建自己需要的兼容css3的代码】

样式	生效	无效
border-radius	为元素四个角设置圆角属性 元素边框	只设置一个角落的圆角属性
box-shadow	模糊大小参数 偏移值	不支持除了黑色(#000)以外的其他颜色
text-shadow	模糊大小参数 偏移值 颜色值	IE下的表现与Firefox/Safari/Chrome有一点点的差异，原因不详