.topbar {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    height: var(--nav-h);
    z-index: 900;
    display: flex;
    align-items: center;
    transition: background 0.3s, border-color 0.3s;
    border-bottom: 1px solid transparent;
}

.topbar.pinned {
    background: rgba(5, 5, 7, 0.88);
    backdrop-filter: blur(10px);
    -webkit-backdrop-filter: blur(10px);
    border-color: var(--border);
}

.topbar-inner {
    display: flex;
    align-items: center;
    justify-content: space-between;
    width: 100%;
}

.topbar-logo {
    font-family: var(--mono);
    font-size: 1.4rem;
    font-weight: 600;
    color: var(--text-0);
    display: flex;
    align-items: center;
    gap: 0.8rem;
}

.topbar-logo img {
    width: 28px;
    height: 28px;
    border-radius: 50%;
}

.topbar-logo span {
    color: var(--text-2);
    font-weight: 400;
}

.topbar-nav {
    display: flex;
    list-style: none;
    gap: 2.4rem;
}

.topbar-nav a {
    color: var(--text-2);
    font-size: 1.25rem;
    font-weight: 500;
    transition: color 0.2s;
}

.topbar-nav a:hover,
.topbar-nav a.active {
    color: var(--text-0);
}

.burger {
    display: none;
    width: 22px;
    height: 16px;
    flex-direction: column;
    justify-content: space-between;
    cursor: pointer;
}

.burger span {
    display: block;
    height: 2px;
    background: var(--text-1);
    border-radius: 1px;
    transition: all 0.3s var(--ease);
}

.burger.open span:nth-child(1) { transform: rotate(45deg) translate(5px, 5px); }
.burger.open span:nth-child(2) { opacity: 0; }
.burger.open span:nth-child(3) { transform: rotate(-45deg) translate(5px, -5px); }

.mobile-menu {
    position: fixed;
    inset: var(--nav-h) 0 0 0;
    background: var(--bg-0);
    display: flex;
    flex-direction: column;
    padding: 3rem 2rem;
    gap: 0;
    transform: translateX(-100%);
    transition: transform 0.35s var(--ease);
    z-index: 800;
    border-top: 1px solid var(--border);
}

.mobile-menu.open {
    transform: translateX(0);
}

.mobile-menu a {
    display: block;
    padding: 1.4rem 0;
    color: var(--text-1);
    font-size: 1.6rem;
    font-weight: 500;
    border-bottom: 1px solid var(--border);
}

.mobile-menu a:last-child { border-bottom: none; }

@media (max-width: 640px) {
    .topbar-nav { display: none; }
    .burger { display: flex; }
}

/* legacy nav compat (writeups pages) */
.header {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    height: var(--nav-h);
    z-index: 900;
    display: flex;
    align-items: center;
    background: rgba(5, 5, 7, 0.88);
    backdrop-filter: blur(10px);
    -webkit-backdrop-filter: blur(10px);
    border-bottom: 1px solid var(--border);
}

.header.scrolled {
    background: rgba(5, 5, 7, 0.95);
}

.nav {
    height: 100%;
    display: flex;
    justify-content: space-between;
    align-items: center;
    max-width: var(--max-w);
    margin: 0 auto;
    padding: 0 2rem;
    width: 100%;
}

.nav-logo {
    display: flex;
    align-items: center;
}

.nav-logo img {
    width: 28px;
    height: 28px;
    border-radius: 50%;
}

.nav-menu {
    display: flex;
}

.nav-list {
    display: flex;
    list-style: none;
    gap: 2.4rem;
}

.nav-link {
    color: var(--text-2);
    font-weight: 500;
    font-size: 1.25rem;
    transition: color 0.2s;
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.nav-link:hover,
.nav-link.active {
    color: var(--text-0);
}

.nav-toggle {
    display: none;
    flex-direction: column;
    justify-content: space-between;
    width: 22px;
    height: 16px;
    cursor: pointer;
}

.nav-toggle span {
    display: block;
    height: 2px;
    background: var(--text-1);
    border-radius: 1px;
    transition: all 0.3s var(--ease);
}

@media (max-width: 640px) {
    .nav-menu {
        position: fixed;
        top: var(--nav-h);
        left: 0;
        width: 100%;
        background: var(--bg-0);
        border-top: 1px solid var(--border);
        transform: translateX(-100%);
        transition: transform 0.35s var(--ease);
    }

    .nav-menu.active {
        transform: translateX(0);
    }

    .nav-list {
        flex-direction: column;
        padding: 2rem;
        gap: 0;
    }

    .nav-item {
        border-bottom: 1px solid var(--border);
    }

    .nav-link {
        padding: 1.4rem 0;
        font-size: 1.5rem;
    }

    .nav-toggle {
        display: flex;
    }
}

.container {
    max-width: var(--max-w);
    margin: 0 auto;
    padding: 0 2rem;
    width: 100%;
}