/* ── Reading progress bar ── */
#reading-progress {
    position: fixed;
    top: 0;
    left: 0;
    height: 2px;
    width: 0%;
    background: linear-gradient(90deg, var(--neon-blue), rgba(0, 243, 255, 0.4));
    box-shadow: 0 0 8px rgba(0, 243, 255, 0.6);
    z-index: 9999;
    transition: width 0.1s linear;
    pointer-events: none;
}

/* ── Back to top button ── */
#back-to-top {
    position: fixed;
    bottom: 2rem;
    right: 2rem;
    width: 44px;
    height: 44px;
    background: var(--glass-bg);
    backdrop-filter: blur(12px);
    -webkit-backdrop-filter: blur(12px);
    border: 1px solid rgba(0, 243, 255, 0.3);
    border-radius: 8px;
    color: var(--neon-blue);
    font-size: 1.4rem;
    line-height: 1;
    cursor: pointer;
    z-index: 9998;
    box-shadow: 0 0 12px rgba(0, 243, 255, 0.15);
    opacity: 0;
    transform: translateY(12px);
    transition: opacity 0.3s, transform 0.3s, box-shadow 0.25s, background 0.25s;
    pointer-events: none;
}

#back-to-top.visible {
    opacity: 1;
    transform: translateY(0);
    pointer-events: auto;
}

#back-to-top:hover {
    background: rgba(0, 243, 255, 0.1);
    box-shadow: 0 0 20px rgba(0, 243, 255, 0.3);
    color: var(--neon-white);
}

@media (max-width: 768px) {
    #back-to-top {
        bottom: 1.25rem;
        right: 1.25rem;
        width: 40px;
        height: 40px;
    }
}