Merhaba arkadaşlar, aşağıda bir css kodu verdim. İçinde 4 adet css expression var. Css expression nedir ve bunları yok edip aynı işlevi gene yaptırabilir miyim? Optimize edilmesi gereken şeyler gibi geldi bana.

#TB_window
{
font:12px "Open Sans",sans-serif;
color:#333
}
#TB_secondLine
{
font:10px "Open Sans",sans-serif;
color:#666
}
.rtl #TB_window,.rtl #TB_secondLine
{
font-family:Tahoma,sans-serif
}
:lang(he-il) .rtl #TB_window,:lang(he-il) .rtl #TB_secondLine
{
font-family:Arial,sans-serif
}
#TB_window a:link
{
color:#666
}
#TB_window a:visited
{
color:#666
}
#TB_window a:hover
{
color:#000
}
#TB_window a:active
{
color:#666
}
#TB_window a:focus
{
color:#666
}
#TB_overlay
{
position:fixed;
z-index:510;
top:0;
left:0;
height:100%;
width:100%
}
.TB_overlayMacFFBGHack
{
background:url(macFFBgHack.png) repeat
}
.TB_overlayBG
{
background-color:#000;
-ms-filter:"alpha(opacity=75)";
filter:alpha(opacity=75);
-moz-opacity:.75;
opacity:.75
}
* html #TB_overlay
{
position:absolute;
height:expression(document.body.scrollHeight>document.body.offsetHeight ? document.body.scrollHeight:document.body.offsetHeight+'px')
}
#TB_window
{
position:fixed;
background:#fff;
z-index:510;
color:#000;
visibility:hidden;
text-align:left;
top:50%;
left:50%;
border:1px solid #555;
-moz-box-shadow:rgba(0,0,0,1) 0 4px 30px;
-webkit-box-shadow:rgba(0,0,0,1) 0 4px 30px;
-khtml-box-shadow:rgba(0,0,0,1) 0 4px 30px;
box-shadow:rgba(0,0,0,1) 0 4px 30px
}
* html #TB_window
{
position:absolute;
margin-top:expression(0 - parseInt(this.offsetHeight/2)+(TBWindowMargin = document.documentElement && document.documentElement.scrollTop || document.body.scrollTop)+'px')
}
#TB_window img#TB_Image
{
display:block;
margin:15px 0 0 15px;
border-right:1px solid #ccc;
border-bottom:1px solid #ccc;
border-top:1px solid #666;
border-left:1px solid #666
}
#TB_caption
{
height:25px;
padding:7px 30px 10px 25px;
float:left
}
#TB_closeWindow
{
height:25px;
padding:11px 25px 10px 0;
float:right
}
#TB_closeAjaxWindow
{
padding:6px 10px 0;
text-align:right;
float:right
}
#TB_closeAjaxWindow a
{
text-decoration:none
}
#TB_ajaxWindowTitle
{
float:left;
padding:6px 10px 0
}
#TB_title
{
background-color:#e8e8e8;
height:27px
}
#TB_ajaxContent
{
clear:both;
padding:2px 15px 15px 15px;
overflow:auto;
text-align:left;
line-height:1.4em
}
#TB_ajaxContent.TB_modal
{
padding:15px
}
#TB_ajaxContent p
{
padding:5px 0 5px 0
}
#TB_load
{
position:fixed;
display:none;
z-index:103;
top:50%;
left:50%;
background-color:#e8e8e8;
border:1px solid #555;
margin:-45px 0 0 -125px;
padding:40px 15px 15px
}
* html #TB_load
{
position:absolute;
margin-top:expression(0 - parseInt(this.offsetHeight/2)+(TBWindowMargin = document.documentElement && document.documentElement.scrollTop || document.body.scrollTop)+'px')
}
#TB_HideSelect
{
z-index:99;
position:fixed;
top:0;
left:0;
background-color:#fff;
border:0;
filter:alpha(opacity=0);
-moz-opacity:0;
opacity:0;
height:100%;
width:100%
}
* html #TB_HideSelect
{
position:absolute;
height:expression(document.body.scrollHeight>document.body.offsetHeight ? document.body.scrollHeight:document.body.offsetHeight+'px')
}
#TB_iframeContent
{
clear:both;
border:0;
margin-bottom:-1px;
_margin-bottom:1px
}
.tb-close-icon
{
height:16px;
margin:-3px -3px 0 0;
width:16px
}
.tb-close-icon:before
{
content:'\f158';
color:#ccc;
font:normal 20px/1 'dashicons';
speak:none;
vertical-align:middle;
-webkit-font-smoothing:antialiased;
-moz-osx-font-smoothing:grayscale
}
.tb-close-icon:hover:before
{
color:#fff
}