Question: I am using GWT HtmlPanel to group the widgets. I want to set the height for the HtmlPanel as 100% using CSS. and set the background-color to it.

**Here it is my code:**

**CSS:**
.loginhtmlpan {
 width: 100%;
 height: 100%;
 background-color: #424242;
}

please help me in this context.

Answer: 
Try using constraint-based CSS positioning rather than specifying specific heights and widths programmatically. This is becoming common practice for standard GWT-widgets. A style like:

.myCssStyle {
 position: absolute;
 top: 0;
 left: 0;
 right: 0;
 bottom: 0;
}

You can then add this style to your HTMLPanel using the addStyleName("myCssStyle") - the nice thing about this is that proper resizing of your HTMLPanel will occur for free when browser resize events occur. As a side note, most GWT "Layout" containers use constraint-based positioning (DockLayoutPanel, LayoutPanel, SplitLayoutPanel, etc).
The simplest way to apply a css style to a gwt widget:

1. Link the stylesheet in your host.html file.
2. call `myHtmlPanel.addStyleName("loginhtmlplan")` when you create the html panel

See <http://google-web-toolkit.googlecode.com/svn/javadoc/2.3/com/google/gwt/user/client/ui/UIObject.html> for more details