Lock ASP.NET Page and Show Animated Image While Waiting for a Long Post-Back

/*
Copyright (c) 2009, Yahoo! Inc. All rights reserved.
Code licensed under the BSD License:
http://developer.yahoo.net/yui/license.txt
version: 2.7.0
*/
/* Remove the dotted border on the resize proxy */
.yui-skin-sam .yui-layout .yui-resize-proxy {
    border: none;
    font-size: 0;
    margin: 0;
    padding: 0;
}
/* During resize, hide the handles */
.yui-skin-sam .yui-layout .yui-resize-resizing .yui-resize-handle {
    visibility: hidden;
}
/* Style the div inside the resize proxy */
.yui-skin-sam .yui-layout .yui-resize-proxy div {
    position: absolute;
    border: 1px solid #808080;
    background-color: #EDF5FF;
}
/* Set the color of the Active resize handle */
.yui-skin-sam .yui-layout .yui-resize .yui-resize-handle-active {
    /*background-color: #EDF5FF;*/
}
/* Styles for the left handle */
.yui-skin-sam .yui-layout .yui-resize-proxy .yui-layout-handle-l {
    width: 5px;
    height: 100%;
    top: 0;
    left: 0;
}
/* Styles for the right handle */
.yui-skin-sam .yui-layout .yui-resize-proxy .yui-layout-handle-r {
    width: 5px;
    top: 0;
    right: 0;
    height: 100%;
    position: absolute;
    zoom: 1;
}
/* Styles for the bottom handle */
.yui-skin-sam .yui-layout .yui-resize-proxy .yui-layout-handle-b {
    width: 100%;
    bottom: 0;
    left: 0;
    height: 5px;
}
/* Styles for the top handle */
.yui-skin-sam .yui-layout .yui-resize-proxy .yui-layout-handle-t {
    width: 100%;
    top: 0;
    left: 0;
    height: 5px;
}

/* Left Collapse button */
.yui-skin-sam .yui-layout .yui-layout-unit-left div.yui-layout-hd .collapse {
    background: transparent url(layout_sprite.png) no-repeat -20px -160px;
    border: 1px solid #808080;
}
/* Left Collapsed Expand Button */
.yui-skin-sam .yui-layout .yui-layout-clip-left .collapse {
    background: transparent url(layout_sprite.png) no-repeat -20px -140px;
    border: 1px solid #808080;
}
/* Right Collapse Button */
.yui-skin-sam .yui-layout .yui-layout-unit-right div.yui-layout-hd .collapse {
    background: transparent url(layout_sprite.png) no-repeat -20px -200px;
    border: 1px solid #808080;
}
/* Right Collapsed Expand Button */
.yui-skin-sam .yui-layout .yui-layout-clip-right .collapse {
    background: transparent url(layout_sprite.png) no-repeat -20px -120px;
    border: 1px solid #808080;
}
/* Top Collapse Button */
.yui-skin-sam .yui-layout .yui-layout-unit-top div.yui-layout-hd .collapse {
    background: transparent url(layout_sprite.png) no-repeat -20px -220px;
    border: 1px solid #808080;
}
/* Top Collapsed Expand Button */
.yui-skin-sam .yui-layout .yui-layout-clip-top .collapse {
    background: transparent url(layout_sprite.png) no-repeat -20px -240px;
    border: 1px solid #808080;
}
/* Bottom Collapse Button */
.yui-skin-sam .yui-layout .yui-layout-unit-bottom div.yui-layout-hd .collapse {
    background: transparent url(layout_sprite.png) no-repeat -20px -260px;
    border: 1px solid #808080;
}
/* Bottom Collapsed Expand Button */
.yui-skin-sam .yui-layout .yui-layout-clip-bottom .collapse {
    background: transparent url(layout_sprite.png) no-repeat -20px -180px;
    border: 1px solid #808080;
}
/* Close Button */
.yui-skin-sam .yui-layout .yui-layout-unit div.yui-layout-hd .close {
    background: transparent url(layout_sprite.png) no-repeat -20px -100px;
    border: 1px solid #808080;
}

/* Give the header a blue backgorund */
.yui-skin-sam .yui-layout .yui-layout-hd {
    background:url(../../../../assets/skins/sam/sprite.png) repeat-x 0 -1400px;
    border: 1px solid #808080;
}
/* Set the background color */
.yui-skin-sam .yui-layout {
    background-color: #EDF5FF;
}
/* Style the text in the header */
.yui-skin-sam .yui-layout .yui-layout-unit div.yui-layout-hd h2 {
    font-weight: bold;
    color: #fff;
    padding: 3px;
}
/* Style the body */
.yui-skin-sam .yui-layout .yui-layout-unit div.yui-layout-bd {
    border: 1px solid #808080;
    border-bottom: none;
    border-top: none;
    *border-bottom-width: 0;
    *border-top-width: 0;
    background-color: #f2f2f2;
    text-align: left;
}
/* Add a border to the bottom of the body because there is no footer */
.yui-skin-sam .yui-layout .yui-layout-unit div.yui-layout-bd-noft {
    border-bottom: 1px solid #808080;
}
/* Add a border to the top of the body because there is no header */
.yui-skin-sam .yui-layout .yui-layout-unit div.yui-layout-bd-nohd {
    border-top: 1px solid #808080;
}

/* Style the Clip */
.yui-skin-sam .yui-layout .yui-layout-clip {
    position: absolute;
    height: 20px;
    background-color: #EDF5FF;
    display: none;
    border: 1px solid #808080;
}
/* Style the footer */
.yui-skin-sam .yui-layout div.yui-layout-ft {
    border: 1px solid #808080;
    border-top: none;
    *border-top-width: 0;
    background-color: #f2f2f2;
}

/* Remove the color from the resize handle */
.yui-skin-sam .yui-layout-unit .yui-resize-handle {
    background-color: transparent;
}
/* Reposition the handles */
.yui-skin-sam .yui-layout-unit .yui-resize-handle-r {
    right: 0;
    top: 0;
    background-image: none;
}
.yui-skin-sam .yui-layout-unit .yui-resize-handle-l {
    left: 0;
    top: 0;
    background-image: none;
}
.yui-skin-sam .yui-layout-unit .yui-resize-handle-b {
    right: 0;
    bottom: 0;
    background-image: none;
}
.yui-skin-sam .yui-layout-unit .yui-resize-handle-t {
    right: 0;
    top: 0;
    background-image: none;
}
/* Add the gripper */
.yui-skin-sam .yui-layout-unit .yui-resize-handle-r .yui-layout-resize-knob,
.yui-skin-sam .yui-layout-unit .yui-resize-handle-l .yui-layout-resize-knob {
    position: absolute;
    height: 16px;
    width: 6px;
    top: 45%;
    left: 0px;
    background: transparent url(layout_sprite.png) no-repeat 0 -5px;
}
/* Add the gripper */
.yui-skin-sam .yui-layout-unit .yui-resize-handle-t .yui-layout-resize-knob,
.yui-skin-sam .yui-layout-unit .yui-resize-handle-b .yui-layout-resize-knob {
    position: absolute;
    height: 6px;
    width: 16px;
    left: 45%;
    background: transparent url(layout_sprite.png) no-repeat -20px 0;
}