Skin variation: blue

Include the following code in your MediaWiki:Common.css (wiki admin rights needed):

/*Fonts nur importieren, wenn Sie Google fonts ab Zeile 7 einbinden wollen*/
@import url(https://fonts.googleapis.com/css?family=Roboto:400,700);
@import url(https://fonts.googleapis.com/css?family=Lato:400,700);

/*Skinning*/

/*Fonts einbinden - müssen über @import definiert worden sein*/

body.mediawiki, body.mediawiki.x-body, #content #bodyContent , #firstHeading, #content #firstHeading {font-family: 'Roboto',"arial",sans-serif;} /*Content and top menus*/
.panel .list-group a.list-group-item span, .bs-panel .list-group a.list-group-item span, #bs-globalactions a.list-group-item span {font-family: 'Roboto',"arial",sans-serif;} /*Main navigation*/

/*Custom menu*/

.bs-custom-menu-header-container,.calumma-toggle-button.bs-custom-menu-header-button {background-color: #111f6a;} /*background color*/
.bs-custom-menu-header-container .bs-custom-menu.header a, .label  {color: #ffffff;}  /*link color*/
.calumma-toggle-button.bs-custom-menu-header-button i::before, .calumma-full-screen-button.bs-full-screen-mode i::before {color:#ffffff} /*arrow on toggle button*/

/*Top bar*/

body.mediawiki header.main-header {background-color:#3a539b;  background-image:linear-gradient( to bottom,#3a539b 0%,#3a539b 50%,#32498a 100% );} /*background color*/
   /* Create and edit buttons */
header .bs-featured-actions .dropdown .btn.btn-primary .icon::before{background-color: #98a7c4;}  /*background*/
header .bs-featured-actions .dropdown .btn.btn-primary:hover .icon::before {background-color: #91bae0} /*hover background*/
header .bs-featured-actions .dropdown .btn.dropdown-toggle::after {color: #98a7c4;} /*arrow color*/
header .bs-featured-actions .dropdown .btn.dropdown-toggle:hover::after {color: #91bae0}  /*hover arrow color*/
  /*Create and edit buttons drop-down menu*/
header .bs-featured-actions .dropdown.open .dropdown-menu, header .bs-featured-actions .dropdown.open .dropdown-menu  {background-color: #3a539b;}  /*background color*/
header .bs-featured-actions .dropdown.open .dropdown-menu::before  {color: #3a539b;}  /*menu arrow color*/
  /*full screen toggle*/
.calumma-full-screen-button i::before {color:#ffffff} 

/*Main navigation*/

body.mediawiki  .navigation-main {background-color:#e9ebee;} /*background color*/
  /* Tabs */
.navigation-main .nav.nav-pills li a, .navigation-main .tab-pane.active .bs-calumma-sidebar-edit-link span   {color:#98a7c4;} /*color*/
.navigation-main .nav.nav-pills li:hover a {color:#3a539b;} /*hover color*/
.navigation-main .nav.nav-pills li.active a {color:#3a539b;} /*active color*/
  /*Nav*/
.navigation-main #bs-sitenavtabs div.tab-content a, .navigation-main #bs-sitenavtabs div.tab-content a:visited, .navigation-main #bs-sitenavtabs div.tab-content a:focus, .navigation-main .tab-pane.active .bs-calumma-sidebar-edit-link:hover span {color:#040404;} /*color menu headers*/
.navigation-main a span,.navigation-main .panel .list-group a.list-group-item i, .navigation-main .bs-panel .list-group a.list-group-item i
{background-color: transparent;color:#040404} /*color menu items and their icons*/

/*Left and right  navigation toggles*/

body .navigation-main .sidebar-toggle[data-toggle~="navigation-main-collapse"] i.navigation-main-collapse::before,body .sitetools-main .sidebar-toggle[data-toggle~="sitetools-main-collapse"] i.sitetools-main-collapse::before {color: #cacaca;}/*regular state */
body .navigation-main .sidebar-toggle[data-toggle~="navigation-main-collapse"] i.navigation-main-collapse:hover::before,body .sitetools-main .sidebar-toggle[data-toggle~="sitetools-main-collapse"] i.sitetools-main-collapse:hover::before {color: #98a7c4;}/*regular state */

/*Login link */

.bs-button-user .bs-personal-not-loggedin, .bs-button-user .bs-personal-not-loggedin a:not(.new), .bs-button-user .bs-personal-not-loggedin a:link:not(.new) {color:#ffffff}	

/*Personal menu */
 @media (min-width: 1001px){
     .bs-button-user .bs-personal-menu-container {background-color: #3a539b;}  /*background color*/
     .bs-button-user #bs-personal-menu .separator  {border-bottom:1.125rem solid #3a539b;} /*Personal menu separators */
}

/*Mobile header buttons*/

@media (max-width: 720px){
.mobile-notifications-button i.mobile-notifications-button::before, header.main-header .navbar a.mobile-search-button::before,.sidebar-toggle[data-toggle~="navigation-main-collapse"] i.navigation-main-collapse::before {color:#ffffff;} /*header bar buttons*/
.mobile-notifications-button i.mobile-notifications-button:hover::before, header.main-header .navbar a.mobile-search-button:hover::before,.sidebar-toggle[data-toggle~="navigation-main-collapse"] i.navigation-main-collapse:hover::before {color:#dddddd;}/*header bar buttons hover*/
.navigation-main a span, .navigation-main .panel .list-group a.list-group-item i, .navigation-main .bs-panel .list-group a.list-group-item i, .bs-mobile-user-button .bs-personal-menu a, .bs-mobile-user-button .bs-personal-menu li.bs-personal-menu-container-user span, .bs-mobile-user-button .bs-personal-menu li.bs-personal-menu-container-user span {
    color: #040404;    font-size: 1.2em;} /*nav items color and size*/
.bs-mobile-user-button .bs-personal-menu-container, .navigation-main #bs-sitenavtabs div.tab-content {background-color:#f1f1f1;} /*Personal menu background*/
.bs-mobile-user-button .bs-personal-menu .separator  {border-bottom:2px solid #e6e9f2;} /*Personal menu separators */
}