You have to enter pure CSS. As far as I know there is no tutorial. Hence a web inspector (available in any browser) and some knowledge about CSS is the way to go.
Just for the record – maybe you want to take a look at my modifications_
http://www.23hq.com/mprove
CSS_
body,
#calendar td, .calendar td { background-color:#222; background-image: url(http://mprove.de/_media/backg/paper3.gif); }
#calendar th.year, .calendar th.year{
border-top-color: transparent;
border-top-width: 0; }
#calendar td.empty, .calendar td.empty
{ background-color:#000 }
#frame, #bottomcontext, #personalnav, .meta-one, .meta-edit-message, .meta-one .meta-table table th, .meta-one .meta-table table td
{ background-color:#303330 !important;
background-image: url(http://mprove.de/_media/backg/paper3.gif);}
.meta-one .meta-table table th { text-align: right; }
#personalnav ul li a { color:#E04A00 }
h2, h3, label,
.phototext, .content, .gray,
#about,
.sidebar-item h2, .sidebar-item h3,
th { color: #afbfcc; }
#tabs li.hover a, #tabs li.active a,
#paging, td { color: #fff;}
#tabs li {
border-bottom-style: solid;
border-bottom-width: 1px; }
.sidebar-item h2, .sidebar-item h3 {
border-bottom: 1px solid #526378;
border-top-style: none;
border-top-width: 0;
border-right-style: none;
border-right-width: 0;
border-left-style: none;
border-left-width: 0; }
#maincontainer a,
h1 a,
table.stream a .gray,
#photosidebar .sidebar-item a {
color: #0087c8;}
#fn_container, .photos-all{
-webkit-box-shadow: #111 2px 2px 10px;
-moz-box-shadow: #111 2px 2px 10px;
box-shadow: #111 2px 2px 10px; }
#sidebar.right{border-width:0 0 0 0 !important;}
table.stream td{border-left:0;}
#globalnav{ background-image: -webkit-gradient(linear, left top, left bottom,
from(#8097cc),
color-stop(0.5, #395daa),
color-stop(0.5, #00618f),
to(rgba( 107, 126, 170, 0.8)));
background-image: -moz-linear-gradient( to bottom,
#8097cc,
#5877b9,
#395daa,
#00618f,
#6B7EAA );
background-image: -ms-linear-gradient( to bottom,
#8097cc,
#5877b9,
#395daa,
#00618f,
#6B7EAA );
background-image: linear-gradient( to bottom,
#8097cc,
#5877b9,
#395daa,
#00618f,
#6B7EAA );
}
#frame { width:100%; max-width:1545px; }
#main { width:auto; max-width:1525px; }
#main #content { padding: 20px 10px; }
#columns {
display: -webkit-flex;
display: flex;
-webkit-flex-flow: row wrap;
flex-flow: row wrap;
-webkit-justify-content: center;
justify-content: center;
}
.column {
float: none !important;
width:auto;
max-width:180px;
max-height:165px;
text-align: center;
padding: 0px 4px 6px 4px;
}
.column .text {
border-bottom-style: none;
border-bottom-width: 0; }
.sidebar-item a.deleteicon,
.sidebar-item a.fotonoteicon,
.sidebar-item a.microblogicon,
.sidebar-item a.deleteicon { background-image: none !important; }
#paging a.small { font-size: 1.5em !important; }
.date, .linkfoot,
a.rotatelefticon, a.rotaterighticon,
.sidebar-item a.facebookicon,
.tag-icon-container,
#themeChoices {
display:none !important;
}
textarea[name=custom_css]{width:1000px !important}
