... ich hatte gestern mal in die CSS vom MLR geguckt, habe es aber auch nicht hin bekommen.

Das "padding" kannst Du ganz raus nehmen, sämtliche Ränder können weg (ich hatte eigentlich alles gelöscht

), dennoch "klebt" das Layout links und rechts bleiben gefühlte 25 Pixel Rand.
Da müsste mal einer unserer CSS Freaks ran und gucken.

... hier ist mal meine:
/*@component-begin @name Default @type Accordion{*/
.ui-accordion {
border: 1px solid black
}
.ui-accordion a {
cursor:pointer;
display:block;
/*border-top: 1px solid #FFFFFF;*/
BORDER-RIGHT: #fff 2px outset;
BORDER-TOP: #fff 2px outset;
BORDER-LEFT: #fff 2px outset;
BORDER-BOTTOM: #fff 2px outset
}
.ui-accordion a.selected {
/*border-bottom: 1px solid black;*/
BORDER-RIGHT: #fff 2px inset;
BORDER-LEFT: #fff 2px inset;
BORDER-BOTTOM: #fff 2px inset;
BORDER-TOP: #fff 2px inset
}
.TogglePaneFancyHeader {
BORDER-RIGHT: #fff 2px inset;
BORDER-LEFT: #fff 2px inset;
BORDER-BOTTOM: #fff 2px inset;
BORDER-TOP: #fff 2px inset
}
.TogglePaneFancyHeaderClosed {
BORDER-RIGHT: #fff 2px outset;
BORDER-TOP: #fff 2px outset;
BORDER-LEFT: #fff 2px outset;
BORDER-BOTTOM: #fff 2px outset
}
.ui-tabs-nav {
list-style: none;
margin: 0;
padding: 0 0 0 4px;
background-color : rgb(228,228,228)
}
.ui-tabs-nav:after {
display: block;
clear: both;
content: " "
}
.ui-tabs-nav li {
float: left;
min-width: 84px /* be nice to Opera */
}
.ui-tabs-nav a{
padding: 0 10px
}
.ui-tabs-nav a span {
padding: 0 10px
}
.ui-tabs-nav a {
margin: 1px 0 0; /* position: relative makes opacity fail for disabled tab in IE */
padding-left: 0;
line-height: 1.2;
text-align: center;
text-decoration: none;
white-space: nowrap; /* required in IE 6 */
outline: 0 /* prevent dotted border in Firefox */
}
.ui-tabs-nav .ui-tabs-selected a {
position: relative;
top: 1px;
z-index: 2;
margin-top: 0;
color: #000
}
.ui-tabs-nav a span {
width: 64px; /* IE 6 treats width as min-width */
min-width: 64px;
height: 18px; /* IE 6 treats height as min-height */
min-height: 18px;
padding-right: 0;
cursor: pointer
}
.ui-tabs-hide {
display: none
}
.ui-tabs-nav * > a span { /* hide from IE 6 */
width: auto;
height: auto
}
/* Additional IE specific bug fixes... */
* html .ui-tabs-nav { /* auto clear, @ IE 6 & IE 7 Quirks Mode */
display: inline-block;
font-weight : normal
}
.ui-tabs-nav *:first-child + html { /* @ IE 7 Standards Mode - do not group selectors, otherwise IE 6 will ignore complete rule (because of the unknown + combinator)... */
display: inline-block
}
/*@component-end}*/