Problem z tłem

Chciałbym aby moje tło działało na podobnej zasadzie co na ten stronie – link, czyli u góry po środku obrazek, reszta w danym kolorze (tutaj białym).

Problem polega na tym, że nie mogę dodać kodu poprzez Custom CSS motywu. Jedyną opcją jaką widzę jest dodanie bezpośrednio do style.css i ponowne wgranie go na stronę.

Aktualnie zrobiłem tak, że cały obraz tła jest w rozmiarze 1920×3500 i nie zdaje to w pełni egzaminu gdyż rozjeżdża się (tło z slajderem) na mniejszych rozdzielczościach innych monitorów.

Kawałek kodu z style.css

* {
	margin: 0;
	padding: 0px;
	font-family: "Open Sans";
}
body {
	background: #f8f8f8;
	margin: 0;
	height: 100%;
	z-index: 1000;
	color: #555;
}
img	{
	border: 0;
	padding: 0 0 0 0;
}
a {
	outline: none;
	font-weight: 600;
}
a:hover, a:visited, a:link, a:active {
	text-decoration: none;
	color: #666;
}
a:hover {
	color: #333;
}
ul, li {
	padding: 0 0 0 0;
	margin: 0;
	list-style-type: none;
}
hr {
	border: 0;
	border-bottom: 1px dashed #ddd;
}
p {
	width: 100%;
	padding: 0 0 0 0;
	margin-bottom: 22px;
	font-family: "Open Sans" !important;
	font-weight: 300;
	font-size: 13px;
	line-height: 24px;
	color: #777;
 	margin-top: 0;
}
strong {
	font-weight: 600;
}
iframe {
	border: none !important;
}
p a {
	color: #333 !important;
}
h1, h2, h3, h4, h5, h6 {
	font-family: "Open Sans" !important;
	font-weight: 500;
	padding: 0 0 0 0;
	margin-top: 0; margin-bottom: 22px; margin-left: auto; margin-right: auto;
	color: #50575E;
	letter-spacing: -0.4px;
}
.entry h1, .entry h2, .entry h3, .entry h4, .entry h5, .entry h6 {
	margin-bottom: 12px;
}
blockquote {
	border-left: 5px solid #ddd;
	padding: 0px 14px 0px 14px;
	margin: 22px 0 22px 22px;
}
blockquote p {
	font-style: italic;
	color: #555;
	font-weight: 500;
}
address, pre {
	margin-bottom: 12px;
	font-size: 12px;
}
.no-space [class*="span"] {
    margin-left: 0;
}
.no-margin {
	margin: 0px !important;
}
.margin-bottom0 {
	margin-bottom: 0px !important;
}
.margin-bottom {
	margin-bottom: 22px;
}
.margin-top {
	margin-top: 22px;
}
.padding-bottom0 {
	padding-bottom: 6px !important;
}
.center {
	text-align: center;
}
.center-position {
	text-align: center;
}
.right {
	text-align: right;
}
.left {
	text-align: left;
}
.float-left {
	float: left;
}
.float-right {
	float: right;
}
.align-left {
	float: left !important;
}
.align-right {
	float: right !important;
}
.center {
	margin-left: auto;
	margin-right: auto;
	text-align: center;
}
.page-template .content-container, .blog .content-container {
	padding-top: 30px;
	padding-bottom: 30px;
}
.single .content-container, .category .content-container, .archive .content-container {
	padding-top: 30px;
	padding-bottom: 30px;
}
.page-template .widget-right, .page-template .widget-left {
	margin-top: -30px;
}
.category .widget-right, .category .widget-left {
	margin-top: -30px;
}
.tag .widget-right, .tag .widget-left {
	margin-top: -30px;
}
.content-container {
	transition: all 1s;
	-webkit-transition: all 1s; /* Safari */
	-ms-transition: all 1s;
	z-index: 3;
	position: relative;
	overflow: hidden;
	background-color: #fff;
	padding-top: 0px;
	padding-bottom: 0px;
}
.content-container > .container {
	padding-top: 0px;
}
.content-heading {
	margin-bottom: 30px;
	font-family: "Open Sans";
	color: #555;
	font-size: 18px;
}
.content-heading a {
	color: #4DD2B8;
	font-weight: 400;
}
.content-heading a:hover {
	color: #444;
}
.heading {
	font-size: 16px;
	font-family: "Open Sans";
	margin-bottom: 0px;
	color: #555;
}
.single .heading {
	font-size: 22px;
	width: 65%;
	display: inline-block;
}
.heading {
	font-size: 16px;
	font-family: "Open Sans";
	margin-bottom: 30px;
	color: #555;
}
.isotope .heading {
	margin-bottom: 6px;
	word-wrap: break-word;
}
.isotope .heading a {
	width: 55%;
	display: inline-block;
}
.heading a {
	color: #51BAB6;
	width: 65%;
	display: inline-block;
	line-height: 28px;
	font-weight: 600;
	transition: all 0.2s;
	-webkit-transition: all 0.2s; /* Safari */
}
.heading a:hover {
	color: #4C5359;
}
.isotope-loadmore {
	margin-bottom: 40px;
	margin-top: 30px;
	width: 100%;
	text-align: center;
	transition: all 0.2s;
	-webkit-transition: all 0.2s; /* Safari and Chrome */

}
.isotope-loadmore a {
	background: #51BABE;
	text-align: center;
	font-size: 10px;
	color: #fff;
	box-sizing: border-box; -moz-box-sizing: border-box; -webkit-box-sizing: border-box;
	transition: all 0.2s;
	-webkit-transition: all 0.2s; /* Safari */
	padding: 14px 18px;
	border-radius: 3px;
	transition: all 0.2s;
	-webkit-transition: all 0.2s; /* Safari and Chrome */
   text-transform: uppercase;
   letter-spacing: 3px;
}
.isotope-loadmore a:hover {
	background: #444;
}
#toTop {
	display:none;
	text-decoration:none;
	position:fixed;
	bottom:30px;
	right:30px;
	overflow:hidden;
	width:50px;
	height:50px;
	border:none;
	text-indent:100%;
	background-color: #111;
	background-image: url(assets/img/backtotop.png);
	background-repeat: repeat;
	background-position: 0px 0px;
	border-radius: 5px;
	z-index: 700;
	transition: all 0.4s;
	-moz-transition: all 0.4s; /* Firefox 4 */
	-webkit-transition: all 0.4s; /* Safari and Chrome */
	-o-transition: all 0.4s; /* Opera */
	z-index: 100000;
}
#toTop:hover {
	background-color: #000;
	background-image: url(assets/img/backtotop.png);
	background-position: 0px -50px;
}
#toTop:active, #toTop:focus {
	outline:none;
}
.no-comments p {
	text-align: center;
}
.entry table {
	border: 1px solid #ddd;
	margin-bottom: 22px;
}
.entry th {
	padding: 14px 18px 14px 18px !important;
	text-align: center !important;
}
.entry tr:first-child {
	border-bottom: 1px solid #ddd;
	background: #f1f1f1;
}
.entry td {
	padding: 14px 18px 14px 18px !important;
	color: #888;
	text-align: center !important;
	font-size: 11.5px;
}
.entry .th-black {
	background: #444;
}
dl {
	font-size: 12px;
}
dt {
	color: #333;
}
dd {
	color: #888;
	margin-bottom: 12px;
}
pre {
	white-space: pre-wrap;       /* css-3 */
	white-space: -moz-pre-wrap;  /* Mozilla, since 1999 */
	white-space: -pre-wrap;      /* Opera 4-6 */
	white-space: -o-pre-wrap;    /* Opera 7 */
	word-wrap: break-word;       /* Internet Explorer 5.5+ */
	background: #f1f1f1;
	padding: 22px 22px 22px 22px;
	border: 1px solid #ccc;
	font-family: "Open Sans" !important;
	font-size: 12px;
	background: #f7f7f7 !important;
	color: #555 !important;
	margin-bottom: 22px;
}
footer {
	z-index: 10000;
}
.hidden {
	position: absolute;
	left: -999999px;
}

pre {
	background: #fff;
	border-radius: 0px;
	border: 1px solid #e7e7e7;
}
.empty-space {
	width: 100%;
	height: 30px;
}
.boxed {
	background: #fff;
	padding: 22px 22px 22px 22px;
}
.drop-shadow {
	position:relative;
}
.drop-shadow:before,
.drop-shadow:after {
    content:"";
    position:absolute;
    z-index:-2;
}
.curved:before {
    top:10px;
    bottom:10px;
    left:0;
    right:50%;
    box-shadow:20px 0 10px #ccc;
    -moz-border-radius:200px / 10px;
    border-radius:100px / 10px;
    top:50;
    bottom:50;
    left:12px;
    right:12px;
    -moz-border-radius:10px / 100px;
    border-radius:20px / 100px;
}

/