Does HTML-Javascript function work on more than one page?

const nav = document.querySelector('.navLinkovi');
const otvorenMeni = document.querySelector('#otvoren');
const zatvorenMeni = document.querySelector('#zatvoren');

const otvoriMeni = () => {
    nav.style.display = 'flex';
    otvorenMeni.style.display = 'none';
    zatvorenMeni.style.display = 'inline-block';
}

otvoren.addEventListener('click', otvoriMeni);

const zatvoriMeni = () => {
    nav.style.display = 'none';
    otvorenMeni.style.display = 'inline-block';
    zatvorenMeni.style.display = 'none';
}

zatvoren.addEventListener('click', zatvoriMeni);

:root {
    --color-primary: #FF7000;

    --color-primary-variant: #e5a55d;
    --color-bg-1: #000e17;
    --color-bg-2: #001e2d;
    --color-bg-3: #012734;
    --color-bg-4: #003347;
    --color-light: #85a2b2;
    --color-white: #fff;

    --container-width-lg: 88%;
    --container-width-md: 92%;

    --transition: all 400ms ease;
}

@font-face { font-family: Poppins; src: url('Poppins-Regular.ttf'); } 
@font-face { font-family: Poppins; font-weight: regular; src: url('Poppins-Regular.ttf');}

* {
    margin: 0;
    padding: 0;
    border: 0;
    outline: 0;
    list-style: none;
    text-decoration: none;
    box-sizing: border-box;
    scroll-behavior: smooth;
}

body {
    font-family: 'Poppins', sans-serif;
    background: #012734;
    color: #fff;
    line-height: 1.7;
}

h1, h2 {
    line-height: 1.1;
    font-weight: 400;
}

h1 {
    font-size: 4rem;
}

h2 {
    font-size: 3.5rem;
}

a {
    color: #fff;
    transition: all 400ms ease;
}

a:hover {
    color: #FF7000;
}

.kontejner {
    width: 88%;
    margin: 0 auto;
    max-width: 2160px;;
}

img {
    display: block;
    object-fit: cover;
    width: 100%;
}

nav {
    height: 5rem;
    width: 100vw;
    display: grid;
    place-items: center;
    position: fixed;
    top: 0;
    left: 0;
    z-index: 99;
}

.nav2 {
    background-color: #001e2d;
    border-bottom: 0.2rem solid #003347;
    box-shadow: 0 1rem 1rem rgba(0, 0, 0, 0.3);
}

.navKontejner {
    height: 100%;
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.navMeni {
    display: none;
    background: transparent;
}

.navMeni img {
    width: 30px;
    height: 30px;
}

.logo {
    width: 5.5rem;
}

.navLinkovi {
    display: flex;
    gap: 4rem;
}

.navSkrol {
    background-color: #001e2d;
    border-bottom: 0.2rem solid #003347;
    box-shadow: 0 1rem 1rem rgba(0, 0, 0, 0.3);
}

.slajdovi {
    display: none;
}

.slajdovi img {
    max-width: 1000px;
    max-height: 500px;
    display: block;
    margin: auto;
    box-shadow: 0 1rem 1rem rgba(0, 0, 0, 0.3);
}

.slajder {
    max-width: 80%;
    position: relative;
    margin: auto;
    margin-top: 80px;
    padding-bottom: 40px
}

header {
    width: 100vw;
    height: 100vh;
    position: relative;
    overflow: hidden;
    background-color: #001e2d;
    border-top: 0.5rem solid #003347;
}

.headerKontejner {
    display: grid;
    grid-template-columns: 40% 40%;
    gap: 10%;
    position: relative;
}

.headerSlika {
    width: 29rem;
    position: relative;
    top: 2rem;
    left: 8rem;
}

.desno {
    display: flex;
    justify-content: center;
    flex-direction: column;
}

.desno h1 {
    text-shadow: 2px 2px 8px rgb(78, 81, 230);
}

.desno p {
    width: 85%;
}

footer {
    border-top: 0.5rem solid #003347;
}

.footerKontejner {
    padding-top: 5rem;
}

.footer {
    display: flex;
    align-items: center;
}

.footerLinkovi {
    margin: 3rem 0 5rem;
    display: flex;
    align-items: center;
    gap: 5rem;
}

/* ---------- O MENI ---------- */

.omeniKontejner {
    margin-top: 300px;
    margin-bottom: 150px;
    padding-left: 250px;
    display: grid;
    grid-template-columns: 26rem auto;
    gap: 3rem;
    position: relative;
}

.naslov {
    position: absolute;
    top: -7rem;
    left: 7rem;
    z-index: 1;
}

.omeniSlika {
    position: relative;
}

.slikaIza {
    width: 16rem;
    height: 24rem;
    position: absolute;
    bottom: 0;
    background-color: #003347;
}

.slikaVelika {
    position: relative;
    left: 1rem;
    bottom: 1rem;
    filter: saturate(0) brightness(0.3);
    transition: 500ms ease;
}

.slikaMala {
    position: absolute;
    top: 3rem;
    left: 8rem;
    height: 22rem;
    width: 22rem;
    overflow: hidden;
    box-shadow: 2rem 2rem 2rem rgba(0, 0, 0, 0.2);
    transition: 500ms ease;
}

.omeniSlika:hover .slikaMala {
    opacity: 0;
}

.omeniSlika:hover .slikaVelika {
    filter: saturate(1) brightness(1);
    box-shadow: 0 3rem 3rem rgba(0, 0, 0, 0.2);
    border: 1rem solid #003347;
    left: 0;
    bottom: 0;
}


.omeniDesno {
    margin-left: 10rem;
}

.omeniDesno p {
    margin: 0 4rem 1.5rem 0rem;
    width: 60%;
}

/* ---------- GALERIJA ---------- */

.galerijaKontejner {
    margin-top: 150px;
    margin-bottom: 150px;
    position: relative;
}

.galerija {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 3rem;
}

.galerija img {
    height: 100%;
    transition: all 400ms ease;
}

.galerija article {
    border: 0.5rem solid #003347;
    transition: all 400ms ease;
}

.galerija article:hover img {
    box-shadow: 0 4rem 4rem rgba(0, 0, 0, 0.5);
    transform: scale(1.1);
}

/* ---------- KONTAKT ---------- */

.kontakt {
    margin-top: 130px;
}

form {
    background: #003347;
    width: 640px;
    margin: 50px auto;
    max-width: 97%;
    border-radius: 4px;
    padding: 55px 30px;
}

.kontaktNaslov h2 {
    letter-spacing: 6px;
    border-bottom: 1px solid white;
    display: inline-block;
    padding-bottom: 8px;
    margin-bottom: 32px;
}

.polovina {
    display: flex;
    justify-content: space-between;
}

.stavka {
    display: flex;
    flex-direction: column;
    margin-bottom: 24px;
    width: 48%;
}

form label {
    display: block;
    font-size: 16px;
    letter-spacing: 3.5px;
    margin-bottom: 5px;
}

.polovina input {
    border-radius: 4px;
    border: 1px solid white;
    outline: 0;
    padding: 16px;
    width: 100%;
    height: 44px;
    background: transparent;
    font-size: 16px;
    color: white;
}

.celo {
    margin-bottom: 24px;
}

.celo textarea {
    background: transparent;
    border-radius: 4px;
    border: 1px solid white;
    outline: 0;
    padding: 12px 16px;
    width: 100%;
    height: 200px;
    font-size: 16px;
    color: white;
}

.dugme {
    margin-bottom: 32px;
}

.dugme input {
    background: transparent;
    border-radius: 4px;
    border: 1px solid white;
    cursor: pointer;
    font-size: 14px;
    font-weight: 600;
    height: 44px;
    letter-spacing: 3px;
    outline: 0;
    padding: 0 20px 0 22px;
    margin-right: 10px;
}

.dugme input[type="submit"], input[type="reset"]{
    background: white;
    color: black;
    transition: all 400ms ease;
}

.dugme input:hover {
    transform: scale(1.1);
}

.stavka input:focus, .celo textarea:focus{
    background: #025069;
}

.ikonice {
    display: flex;
    gap: 1rem;
}

.ikonice img {
    height: 40px;
    width: 40px;
}

/* ---------- RESPONZIVNOST (tablet) ---------- */

@media screen and (max-width: 1024px) {
    .kontejner {
        width: 92%;
        position: relative;
    }

    h1 {
        font-size: 2.5rem;
        line-height: 1.3;
    }

    h2 {
        font-size: 2.5rem;
    }

    .navLinkovi {
        position: absolute;
        top: 100%;
        right: 0;
        flex-direction: column;
        gap: 0;
        display: none;
    }

    .navLinkovi li {
        height: 5rem;
        box-shadow: -3rem 3rem 3rem rgba(0, 0, 0, 0.7);
    }

    .navLinkovi li a {
        background: #003347;
        height: 100%;
        width: 100%;
        display: flex;
        align-items: center;
        padding: 1rem 5rem 1rem 3rem;
        border-top: 1px solid #001e2d;
    }

    .navMeni {
        display: inline-block;
        font-size: 2rem;
        cursor: pointer;
    }

    #zatvoren {
        display: none;
    }

    .slajdovi img {
        max-width: 600px;
        max-height: 300px;
    }

    header {
        height: fit-content;
        padding: 14rem 0 12rem;
        display: grid;
        place-items: center;
    }

    .headerKontejner {
        grid-template-columns: 40% 54%;
        gap: 6%;
        margin: 0;
    }

    .headerSlika {
        width: 100%;
        top: 0;
        left: 0;
    }

    .desno p {
        width: 100%;
    }

    .omeniKontejner {
        grid-template-columns: 40% 54%;
        gap: 6%;
        padding-left: 50px;
    }

    .slikaIza, .slikaMala {
        display: none;
    }

    .slikaVelika {
        left: 0;
        top: 0;
        filter: saturate(1) brightness(1);
    }

    .slikaVelika:hover {
        border: none;
    }

    .omeniDesno {
        margin: 0;
    }

    .omeniDesno p {
        margin-bottom: 1rem;
        width: 90%;
    }

    .galerijaKontejner {
        width: 90%;
    }

    .galerija {
        grid-template-columns: repeat(2, 1fr);
    }


}

/* ---------- RESPONZIVNOST (telefon) ---------- */

@media (max-width: 600px) {
    
    h1, h2 {
        font-size: 2rem;
        line-height: 1.3;
    }

    .slajdovi img {
        max-width: 500px;
        max-height: 180px;
    }

    header {
        padding: 0;
        padding-bottom: 6rem;
    }

    .headerKontejner {
        grid-template-columns: 1fr;
        gap: 1rem;
        text-align: center;
    }

    .headerSlika {
        width: 70%;
        height: 70%;
        margin: 0 auto;
        margin-top: 7rem;
        overflow: hidden;
    }

    .desno p {
        margin-top: 1rem;
    }

    .omeniKontejner {
        grid-template-columns: 1fr;
        gap: 2rem;
        padding-left: 10px;
        margin-top: 230px;
    }

    .omeniDesno p {
        width: 100%;
    }

    .omeniSlika {
        display: flex;
        justify-content: center;
        align-items: center;
    }

    .slikaVelika {
        height: 50%;
        width: 50%;
    }

    .slikaIza, .slikaMala {
        display: none;
    }

    .omeniSlika:hover .slikaVelika {
        filter: saturate(1) brightness(1);
        box-shadow: 0 0 0 0;
        border: none;
    }
    
    .polovina {
        flex-direction: column;
    }

    .stavka {
        width: 100%;
    }

    .dugme {
        display: flex;
        flex-direction: column;
    }

    .dugme input {
        margin-bottom: 10px;
        width: 100%;
    } 

    .footer h2 {
        font-size: 1.5rem;
    }

    .footer {
        display: flex;
        justify-content: center;
        align-items: center;
    }

    .footerLinkovi {
        flex-direction: column;
        gap: 1rem;
        margin-top: 5rem;
    }
}

/* ---------- SVETLA TEMA ---------- */

.dark-mode {
    background: white;
}

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Nikola Photo</title>
    <link rel="stylesheet" href="style.css">
</head>
<body>
    <nav>
        <div class="kontejner navKontejner">
            <a href="index.html" class="logo"><img src="slike/logo.png" alt="logo"></a>
            <ul class="navLinkovi">
                <li><a href="index.html">Pocetna</a></li>
                <li><a href="galerija.html ">Galerija</a></li>
                <li><a href="omeni.html">O meni</a></li>
                <li><a href="kontakt.html">Kontakt</a></li>
            </ul>
            <button class="navMeni" id="otvoren"><img src="slike/hamburger.png" alt=""></button>
            <button class="navMeni" id="zatvoren"><img src="slike/xicon.png" alt=""></button>
        </div>
    </nav> 

    <div class="slajder">
        <div class="slajdovi">
            <img src="slike/slika10.png" alt="">
        </div>
        <div class="slajdovi">
            <img src="slike/slika11.png" alt="">
        </div>
        <div class="slajdovi">
            <img src="slike/slika17.jpg" alt="">
        </div>
    </div>

    <header id="header">
        <div class="kontejner headerKontejner">
            <div class="levo">
                <div class="headerSlika">
                    <img src="slike/slika8.png" alt="pariz">
                </div>
            </div>
            <div class="desno">
                <h1>NikolaPhoto</h1><br>
                <p>Lorem, ipsum dolor sit amet consectetur adipisicing elit. Sapiente ut praesentium assumenda cum et? Fugit quae dolor animi enim eveniet, alias hic nulla eius nam accusamus facilis asperiores rerum odit.</p>
            </div>
        </div>
    </header>

    <footer>
        <div class="kontejner footerKontejner">
            <div class="footer">
                <h2 class="footerNaslov">[email protected]</h2>
            </div>
            <ul class="footerLinkovi">
                <li><a href="index.html">Pocetna</a></li>
                <li><a href="galerija.html ">Galerija</a></li>
                <li><a href="omeni.html">O meni</a></li>
                <li><a href="kontakt.html">Kontakt</a></li>
            </ul>
        </div>
        <button type="button" onclick="themeToggle()">Theme Toggle</button><div id="theme"></div>
    </footer>

    <script src="script.js"></script>
</body>
</html>