Use CSS3 rule sets instead of images as a style sheet file is much smaller, especially when compressed.
In addition, calling a style sheet only generates one HTTP request, whereas each image generates an HTTP request.
Rounded corners for boxes should be generated in CSS3 rather than by images.
Use the following:
#cadre { border-radius: 10px; }
<div id="cadre">
<p>
Lorem ipsum dolor sit amet, consectetur adipiscing elit.
</p>
</div>