/* Blue sidebar background */
    .wy-side-nav-search,
    .wy-nav-side {
        background: #004080;
    }

    /* High-contrast expand/collapse arrows */
    .wy-menu-vertical .toctree-expand::before,
    .wy-menu-vertical .toctree-l1 > a::before,
    .wy-menu-vertical .toctree-l2 > a::before,
    .wy-menu-vertical .toctree-l3 > a::before {
        color: gray !important;
        font-weight: bold;
        font-size: 120% !important;
    }

    /* Change expanded TOC background to light blue */
    .wy-menu-vertical li.toctree-l1.current > a,
    .wy-menu-vertical li.toctree-l2.current > a,
    .wy-menu-vertical li.toctree-l3.current > a,
    .wy-menu-vertical li.toctree-l4.current > a,
    .wy-menu-vertical li.toctree-l1.current > ul,
    .wy-menu-vertical li.toctree-l2.current > ul,
    .wy-menu-vertical li.toctree-l3.current > ul,
    .wy-menu-vertical li.toctree-l4.current > ul {
        background-color: #ccdbfc !important;   /* azure Light blue */
    }