Switch to Mountain theme from settings and add this to your Stylish extension styles.

tbconline.ge.css

@import url(https://fonts.googleapis.com/css?family=Roboto:400,300,500,700);

.MountainScheme {
	background: url('http://i.imgur.com/aLevwFr.jpg') no-repeat center top fixed !important;
	background-size: cover !important;
}

body.MountainScheme {
	font-family: Roboto, 'Helvetica Neue', Helvetica, sans-serif !important;
}

.MountainScheme.private-page #heading .logo {
    background-position: 24px 19px !important
}

body.MountainScheme #wrapper {
    /* zoom: 1.1*/
}

body.MountainScheme .portlet-radius, body.MountainScheme .portlet-fill {
    background: none !important;
}

.MountainScheme .portlet, .collapseHeader {
    border-radius:2px !important;
}

.MountainScheme .portlet {
	-webkit-backdrop-filter: blur(20px);
    background-color: rgba(255,255,255,0.7) !important;
}

.odd-radius-column-first, .even-radius-column-first, .odd-radius-column-big-first, .even-radius-column-big-first, .odd-radius-column-last, .even-radius-column-last, .odd-radius-column-big-last, .even-radius-column-big-last {
    border-radius:0px;
}

.actionButton-menu-top,
.actionButton-menu-top-left,
.actionButton-menu-top-right,
.actionButton-menu-top-middle,
.actionButton-menu-middle,
.actionButton-menu-middle-left,
.actionButton-menu-content,
.actionButton-menu-middle-right,
.actionButton-menu-bottom
.actionButton-menu-bottom-left,
.actionButton-menu-bottom-right,
.actionButton-menu-bottom-middle
{
    background: none !important;
}

.actionButton-menu {
    -webkit-backdrop-filter: blur(20px);
    background: rgba(255,255,255,0.7) !important;
    border-radius: 0;
}