.header{

    position:fixed;

    top:0;
    left:0;

    width:100%;

    display:flex;

    justify-content:space-between;
    align-items:center;

    padding:18px 32px;

    background:rgba(15,23,42,.75);

    backdrop-filter:blur(14px);

    -webkit-backdrop-filter:blur(14px);

    border-bottom:1px solid var(--border);

    z-index:1000;

}

[data-theme="light"] .header{

    background:rgba(255,255,255,.75);

}

.logo{

    font-size:1.4rem;

    font-weight:700;

    color:var(--primary);

    letter-spacing:.5px;

}

.header nav{

    display:flex;

    align-items:center;

    gap:28px;

}

.header nav a{

    position:relative;

    color:var(--text-secondary);

    font-weight:500;

    transition:var(--transition);

}

.header nav a:hover,

.header nav a.active{

    color:var(--primary);

}

.header nav a::after{

    content:"";

    position:absolute;

    left:0;
    bottom:-6px;

    width:0;

    height:2px;

    background:var(--primary);

    transition:var(--transition);

}

.header nav a:hover::after,

.header nav a.active::after{

    width:100%;

}

.theme-btn{

    width:46px;

    height:46px;

    display:flex;

    justify-content:center;
    align-items:center;

    border-radius:50%;

    background:var(--surface);

    color:var(--text);

    border:1px solid var(--border);

    transition:var(--transition);

}

.theme-btn:hover{

    background:var(--primary);

    color:#fff;

    transform:rotate(180deg);

}

@media (max-width:768px){

    .header{

        padding:16px 20px;

    }

    .header nav{

        gap:16px;

    }

    .header nav a{

        font-size:.9rem;

    }

}