I tried changing the parameters but not without an effect,
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Source Files

panel-skin.css

panel.css

yuicss.lib
.yui3-skin-sam .yui3-panel .yui3-widget-hd {

padding: 8px 28px 8px 8px; / Room for close button. /

min-height: 13px; / For the close button /

_height: 13px; / IE6 /

color: white;

background-color: #3961c5;

background: -moz-linear-gradient(

0% 100% 90deg,

2647a0 7%,

3d67ce 50%,

426fd9 100%

);

background: -webkit-gradient(

linear,

left bottom,

left top,

from(#2647a0),

color-stop(0.07, #2647a0),

color-stop(0.5, #3d67ce),

to(#426fd9)

);

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I would change the modal screen, height, width and color
follows an example screen

Thanks in advanced

Changed line 1567 and 1568 in (yuicss.lib )
.yui3-skin-sam .yui3-panel-content{-webkit-box-shadow:0 0 5px #333;-moz-box-shadow:0 0 5px #333;box-shadow:0 0 5px #333;border:10px solid #202020;background:white;width: 800px ; height: 450px}

.yui3-skin-sam .yui3-panel .yui3-widget-hd{padding:8px 28px 8px 8px;min-height:13px;_height:13px;color:white;background-color:#F5F5F5;background:-moz-linear-gradient(0% 100% 90deg,#F5F5F5 7%,#F5F5F5 50%,#F5F5F5 100%);background:-webkit-gradient(linear,left bottom,left top,from(#F5F5F5),color-stop(0.03,#F5F5F5),color-stop(0.5,#F5F5F5),to(#F5F5F5))}
Thanks Team Support