hugo-theme-relearn/static/css/theme-blue.css

:root{
    
    --MAIN-TEXT-color:#323232; /* Color of text by default */
    --MAIN-TITLES-TEXT-color: #5e5e5e; /* Color of titles h2-h3-h4-h5 */
    --MAIN-LINK-color:#1C90F3; /* Color of links */
    --MAIN-LINK-HOVER-color:#167ad0; /* Color of hovered links */

    --MENU-HEADER-BG-color:#1C90F3; /* Background color of menu header */
    --MENU-HEADER-BORDER-color:#33a1ff; /*Color of menu header border */ 

    --MENU-SEARCH-BG-color:#167ad0; /* Search field background color (by default borders + icons) */
    --MENU-SEARCH-BOX-color: #33a1ff; /* Override search field border color */
    --MENU-SEARCH-BOX-ICONS-color: #a1d2fd; /* Override search field icons color */

    --MENU-SECTIONS-ACTIVE-BG-color:#20272b; /* Background color of the active section and its childs */
    --MENU-SECTIONS-BG-color:#252c31; /* Background color of other sections */
    --MENU-SECTIONS-LINK-color: #ccc; /* Color of links in menu */
    --MENU-SECTIONS-LINK-HOVER-color: #e6e6e6;  /* Color of links in menu, when hovered */
    --MENU-SECTION-ACTIVE-CATEGORY-color: #777; /* Color of active category text */
    --MENU-SECTION-ACTIVE-CATEGORY-BG-color: #fff; /* Color of background for the active category (only) */

    --MENU-VISITED-color: #33a1ff; /* Color of 'page visited' icons in menu */
    --MENU-SECTION-HR-color: #20272b; /* Color of <hr> separator in menu */
    
}

body {
    color: var(--MAIN-TEXT-color) !important;
}

h2, h3, h4, h5 {
    color: var(--MAIN-TITLES-TEXT-color) !important;
}

a {
    color: var(--MAIN-LINK-color);
}

a:hover {
    color: var(--MAIN-LINK-HOVER-color);
}

#sidebar ul li.visited > a .read-icon {
	color: var(--MENU-VISITED-color);
}

#body a.highlight:after {
    display: block;
    content: "";
    height: 1px;
    width: 0%;
    -webkit-transition: width 0.5s ease;
    -moz-transition: width 0.5s ease;
    -ms-transition: width 0.5s ease;
    transition: width 0.5s ease;
    background-color: var(--MAIN-HOVER-color);
}
#sidebar {
	background-color: var(--MENU-SECTIONS-BG-color);
}
#sidebar #header-wrapper {
    background: var(--MENU-HEADER-BG-color);
    color: var(--MENU-SEARCH-BOX-color);
    border-color: var(--MENU-HEADER-BORDER-color);
}
#sidebar .searchbox {
	border-color: var(--MENU-SEARCH-BOX-color);
    background: var(--MENU-SEARCH-BG-color);
}
#sidebar ul.topics > li.parent, #sidebar ul.topics > li.active {
    background: var(--MENU-SECTIONS-ACTIVE-BG-color);
}
#sidebar .searchbox * {
    color: var(--MENU-SEARCH-BOX-ICONS-color);
}

#sidebar a {
    color: var(--MENU-SECTIONS-LINK-color);
}

#sidebar a:hover {
    color: var(--MENU-SECTIONS-LINK-HOVER-color);
}

#sidebar ul li.active > a {
    background: var(--MENU-SECTION-ACTIVE-CATEGORY-BG-color);
    color: var(--MENU-SECTION-ACTIVE-CATEGORY-color) !important;
}

#sidebar hr {
    border-color: var(--MENU-SECTION-HR-color);
}