<div style="filter:alpha(opacity=50);background:#ffffff;width:600;">
<span style="color:yellow">图层背景半透明，字体颜色也半透明</span>
</div>
<div style="filter:alpha(opacity=50);background:#ffffff;width:600">
<span style="position:relative;color:yellow">图层背景半透明，字体颜色不半透明</span>
</div>