The high society theme, that yellow is an image in the images/ directory, you can just replace it with this line:
body.scheme-high #page-wrap {
background: url('images/background-high-page-wrap.jpg') top repeat-x;
}
Just replace the url(‘ with whatever URL your own image is, you can grab that image from the directory and modify it as you wish but don’t put it back into the same directory, put it someplace else so that when the theme updates you don’t lose it.
the background for the menubar you have right now is:
body.scheme-ceasel #menubar-wrapper {
margin: 5px auto;
width: 98.2%;
background: #5e5e5e; /* Old browsers */
background: -moz-linear-gradient(top, #8a8a8a 0%, #707070 49%, #5e5e5e 51%, #777777 100%); /* FF3.6+ */
background: -webkit-gradient(linear, left top, left bottom, color-stop(0%,#8a8a8a), color-stop(49%,#707070), color-stop(51%,#5e5e5e), color-stop(100%,#777777)); /* Chrome,Safari4+ */
background: -webkit-linear-gradient(top, #8a8a8a 0%,#707070 49%,#5e5e5e 51%,#777777 100%); /* Chrome10+,Safari5.1+ */
background: -o-linear-gradient(top, #8a8a8a 0%,#707070 49%,#5e5e5e 51%,#777777 100%); /* Opera11.10+ */
background: -ms-linear-gradient(top, #8a8a8a 0%,#707070 49%,#5e5e5e 51%,#777777 100%); /* IE10+ */
-moz-border-radius: 4px;
-khtml-border-radius: 4px;
-webkit-border-radius: 4px;
border-radius: 4px;
color: #fff;
text-decoration: none;
text-shadow: -1px -1px 0 rgba(0, 0, 0, 0.15);
overflow: visible;
-moz-box-shadow: 1px 1px 3px rgba(0, 0, 0, 0.2), 1px 1px 3px rgba(0, 0, 0, 0.2) inset;
-webkit-box-shadow: 1px 1px 3px rgba(0, 0, 0, 0.2), 1px 1px 3px rgba(0, 0, 0, 0.2) inset;
box-shadow: 1px 1px 3px rgba(0, 0, 0, 0.2), 1px 1px 3px rgba(0, 0, 0, 0.2) inset;
-webkit-appearance: none;
padding: 6px 5px 5px;
border: solid 1px #666;
}
Notice the plethora of webkite gradients up there, but, if you use the edit-css module from jetpack you can just override it with:
body.scheme-ceasel #menubar-wrapper {
background-color: Transparent;
}
Or find a guide online to doing css gradients there’s some tools that will give you the code to replace it whenever you want.
There’s also a border: in there and such you can set to none; or 0