JSFiddle - React, Tailwind, and code Playground

HTML

<!DOCTYPE HTML>
<html>
    <head>
        <meta charset="utf-8"/>
        <title>Strona Testowa</title>
        <meta name="description" content="Strona Testowa"/>
        <meta name="keywords" content="test, strona, html"/>
        <meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1"/>
        <meta name="viewport" content="width=device-width, initial-scale=1.0">        
        <link rel="stylesheet" type="text/css" href="style.css">
        <script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.4/jquery.min.js"></script>
        <script type="text/javascript" src="script.js"></script>
        <script async defer src="https://maps.googleapis.com/maps/api/js?key=AIzaSyC9fp1zZENEQMqvKurhc3AZQaNTy_gYmfY&callback=initMap"></script>
        <link href='https://fonts.googleapis.com/css?family=Lato&subset=latin,latin-ext' rel='stylesheet' type='text/css'>
        <script src="jquery.scrollTo.min.js"></script>
    </head>

    <body>
        <div id="header">
            <img src="logo.png"/>
        </div>

        <ul id="flagsul">
            <img class="flag" style="margin-right: 20%;" src="lang/pl.png"/>
            <img class="flag" style="margin-right: 10%;" src="lang/uk.png"/>
        </ul>

        <div id="nav">
            <ul>
                <a id="o1" href="#"><li>O nas</li></a>
                <a id="o2" href="#"><li>Zespół</li> </a>
                <a id="o3" href="#"><li>Katalog</li> </a>
                <a id="o4" href="#"><li>Lokalizacja</li> </a>
                <a id="o5" href="#"><li style="border:none">Kontakt</li></a>
            </ul>
        </div>

        <div id="break"></div>

        <div id="content">
            <span id="onas"></span>
            <h1>O nas</h1>
            <div id="break2"></div>
            <img id="salon" src="salon.png"/>
            <p id="onaspl">Lorem ipsum dolor sit amet, consectetur adipiscing elit. 
            Cras ac urna sed lorem scelerisque cursus et mollis felis. 
            Etiam a...

CSS

body {
    background: url(tlo.jpg) no-repeat center fixed; 
    -webkit-background-size: cover;
    -moz-background-size: cover;
    -o-background-size: cover;
    background-size: cover;
}

a{
    color:black;
    text-decoration: none;
}

h1{
    text-align: center;
    font-style: italic;
}

p{
    margin-left: auto;
    margin-right: auto;
    font-size: 20px;
    margin-top: 45px;
    width:50%;
}

#header {
    height: 100px;    
    margin-top: 50px;
    font-size: 50px;
    font-weight: bold;
    text-align: center;    
    margin-bottom: 50px;
}

#header img{
    height: 80%;
    margin-left: auto;
    margin-right: auto;
    -webkit-box-shadow: 0px 5px 14px 12px rgba(0,0,0,0.75);
    -moz-box-shadow: 0px 5px 14px 12px rgba(0,0,0,0.75);
    box-shadow: 0px 5px 14px 12px rgba(0,0,0,0.75);
}

#break{
    margin-left: auto;
    margin-right: auto;
    width: 80%;
    height: 1px;
    background-color: black;
}

#break2{
    margin-top: -10px;
    margin-bottom: 30px;
    margin-left: auto;
    margin-right: auto;
    width: 30%;
    height: 1px;
    background-color: black;
}

#nav ul{
    margin-left: auto;
    margin-right: auto;
    text-align: center;
    font-size: 27px;
    list-style: none;
}

#nav ul li{
    text-align: center;
    padding: 7px;
    display: inline;
    border-right: 2px solid black;
}

#nav ul li:nth-child(4) {
    border-right:none;
}

#nav a:hover{
    font-weight: bold;
}

#content {
    margin-top: 100px;
    text-align: center;
    width: 80%;
    margin-left: auto;
    margin-right: auto;
}

#salon{
    border-radius: 20%;
    margin-left: auto;
    margin-right: auto;
    -webkit-box-shadow: 8px 9px 38px 22px rgba(0,0,0,0.75);
    -moz-box-shadow: 8px 9px 38px 22px rgba(0,0,0,0.75);
    box-shadow: 8px 9px 38px 22px rgba(0,0,0,0.75);
}

#staff{
    margin-top: 40px;
    list-style: none;
    display: inline-block;
}

#staff li{
    display: inline-block;
    margin: 0px 45px 0px 45px;
}

#staff img{
    border-radius: 90%;...

JavaScript

//staff

$(function()
{
    $('#staff1').hover(function(){
        $('#staff1').attr('src', 'staff1c.png');
        $('#desc1').fadeIn();
    }),
    $('#staff1').mouseleave(function(){
        $('#staff1').attr('src', 'staff1.jpg');
        $('#desc1').hide(1);
    })
});

$(function()
{
    $('#staff2').hover(function(){
        
        $('#staff2').attr('src', 'staff2c.png');
        $('#desc2').fadeIn();
    }),
    $('#staff2').mouseleave(function(){
        $('#staff2').attr('src', 'staff2.png');
        $('#desc2').hide(1);
    })

});

$(function()
{
    $('#staff3').hover(function(){
        $('#staff3').attr('src', 'staff3c.png');
        $('#desc3').fadeIn();
    }),
    $('#staff3').mouseleave(function(){
        $('#staff3').attr('src', 'staff3.jpg');
        $('#desc3').hide(1);
    })
});

// staff opis 

// katalog

var index = 1;

function plusIndex(n){
    index += n;
    showImage(index);
}

function showImage(n){
    var x = document.getElementsByClassName('slides');
    if(n>x.length)index=1;
    if(n<1)index=x.length;
    for(var i=0; i<x.length; ++i){
        x[i].style.display = "none";
    };
    x[index-1].style.display = "block";
}

function initMap(){
    var loc = {lat:53.487201 ,lng:-2.093636};
    var map = new google.maps.Map(document.getElementById('map'), {
        zoom: 12,
        center: loc
    });
    var marker = new google.maps.Marker({
        position: loc,
        map: map
    });
};

$(function(){
    $('#o1').click(function() {
        $.scrollTo($('#onas'), 500);
    });
    $('#o2').click(function(){
        $.scrollTo($('#linkstaff'), 500);
    });
    $('#o3').click(function(){
        $.scrollTo($('#linkkatalog'), 500);
    });
    $('#o4').click(function() {
        $.scrollTo($('#map'), 500);
    });
    $('#o5').click(function() {
        $.scrollTo($('#map'), 500);
    });
})