Not all widgets will be that easy. I specify most of the ID names, background, and overlay images in css file... where I can specify properties like width and height in the style sheet. Then I can call the ID names from the css from the Wallpaper.html:
example: Wallpaper.html
<div id="background_image"></div>
example for 6+: Style.css
#background_image {
position: absolute;
background: url('../Images/wallpaper_img.png') center no-repeat;
background-size: 414px 736px;
top:0px;
left: 0px;
width: 414px;
height: 736px;
opacity: 1.0;
z-index: 30;
}
For some widgets... they call the overlay images in the Wallpaper.html... and specify the width and height there.
example:
<img src="Images/wallpaper.png" width="414" height="736" style="position: absolute; top: 0px; left: 0px; z-index:30;">
EDIT: Sital is another person I would listen to.