javascript – Como faço pra alterar a cor de fundo do site?

Galera beleza? fiz uma page em html css javascript que quando clico na cor do tênis eu mudo a cor , agora queria saber que código eu adiciono pra mudar a cor do fundo background junto com a cor do tênis sendo a mesma cor que eu cliquei?

!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <link rel="stylesheet" href="style.css">
    <script src="https://kit.fontawesome.com/a81368914c.js"></script>
    <link href="https://fonts.googleapis.com/css?family=Poppins:200,300,400,500,600,700&display=swap" rel="stylesheet">
    <title>Produto</title>
</head>

<body>
    <div class="container">
        <div class="card">
            <div class="shoeBackground">
                <div class="gradients">
                    <div class="gradient second" color="blue"></div>
                    <div class="gradient" color="red"></div>
                    <div class="gradient" color="green"></div>
                    <div class="gradient" color="orange"></div>
                    <div class="gradient" color="black"></div>
                </div>
                <h1 class="nike">nike</h1>
                <img src="img/logo.png" alt="" class="logo">
                <a href="#" class="share"><i class="fas fa-share-alt"></i></a>

                <img src="img/blue.png" alt="" class="shoe show" color="blue">
                <img src="img/red.png" alt="" class="shoe" color="red">
                <img src="img/green.png" alt="" class="shoe" color="green">
                <img src="img/orange.png" alt="" class="shoe" color="orange">
                <img src="img/black.png" alt="" class="shoe" color="black">

            </div>
            <div class="info">
                <div class="shoeName">
                    <div>
                        <h1 class="big">Nike Zoom KD 12</h1>
                        <span class="new">new</span>
                    </div>
                    <h3 class="small">Tenis para corridas</h3>
                </div>
                <div class="description">
                    <h3 class="title">Product Info</h3>
                    <p class="text">Abrindo novos caminhos para os atletas, KD fornece acesso sem precedentes à sua vida por meio de seu canal no YouTube.</p>
                </div>
                <div class="color-container">
                    <h3 class="title">Cor</h3>
                    <div class="colors">
                        <span class="color active " primary="#2175f5" color="blue"></span>
                        <span class="color" primary="#f84848" color="red"></span>
                        <span class="color" primary="#29b864" color="green"></span>
                        <span class="color" primary="#ff5521" color="orange"></span>
                        <span class="color " primary="#444" color="black"></span>
                    </div>
                </div>
                <div class="size-container">
                    <h3 class="title">tamanho</h3>
                    <div class="sizes">
                        <span class="size">38</span>
                        <span class="size">39</span>
                        <span class="size active">40</span>
                        <span class="size">41</span>
                        <span class="size">42</span>
                    </div>
                </div>
                <div class="buy-price">
                    <a href="#" class="buy"><i class="fas fa-shopping-cart"></i>Carrinho</a>
                    <div class="price">
                        <p>R$</p>
                        <h1>599.99</h1>
                    </div>
                </div>
            </div>
        </div>
    </div>

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

javascript

const sizes = document.querySelectorAll('.size');
const colors = document.querySelectorAll('.color');
const shoes = document.querySelectorAll('.shoe');
const gradients = document.querySelectorAll('.gradient');
const shoeBg = document.querySelector('.shoeBackground');



let prevColor = "blue";
let animationEnd = true;

function changeSize(){
    sizes.forEach(size => size.classList.remove('active'));
    this.classList.add('active');
}

function changeColor(){
    if(!animationEnd) return;
    let primary = this.getAttribute('primary');
    let color = this.getAttribute('color');
    let shoe = document.querySelector(`.shoe(color="${color}")`);
    let gradient = document.querySelector(`.gradient(color="${color}")`);
    let prevGradient = document.querySelector(`.gradient(color="${prevColor}")`);

    if(color == prevColor) return;

    colors.forEach(c => c.classList.remove('active'));
    this.classList.add('active');

    document.documentElement.style.setProperty('--primary', primary);
    
    shoes.forEach(s => s.classList.remove('show'));
    shoe.classList.add('show');

    gradients.forEach(g => g.classList.remove('first', 'second'));
    gradient.classList.add('first');
    prevGradient.classList.add('second');

    prevColor = color;
    animationEnd = false;

    gradient.addEventListener('animationend', () => {
        animationEnd = true;
    })
}

sizes.forEach(size => size.addEventListener('click', changeSize));
colors.forEach(c => c.addEventListener('click', changeColor));

let x = window.matchMedia("(max-width: 1000px)");

function changeHeight(){
    if(x.matches){
        let shoeHeight = shoes(0).offsetHeight;
        shoeBg.style.height = `${shoeHeight * 0.9}px`;
    }
    else{
        shoeBg.style.height = "475px";
    }
}

changeHeight();

window.addEventListener('resize', changeHeight); 

css

:root{
    --primary: #2175f5;
}

*{
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    font-family: 'Poppins', sans-serif;
}



.container{
    min-height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
    padding: 40px;
    overflow: hidden;
}

.card{
    display: flex;
    justify-content: center;
    align-items: center;
    width: 860px;
}

.shoeBackground{
    position: relative;
    width: 50%;
    height: 475px;
    box-shadow: -15px 0 35px rgba(0, 0, 0, 0.1),
    0 -15px 35px rgba(0, 0, 0, 0.1),
    0 15px 35px rgba(0, 0, 0, 0.1);
    transition: .5s;
}

.gradients{
    position: absolute;
    width: 100%;
    height: 100%;
    left: 0;
    top: 0;
}

.gradient{
    position: absolute;
    width: 100%;
    height: 100%;
    left: 0;
    top: 0;
    z-index: -2;
}

.first{
    z-index: 0;
    animation: 1s width ease;
}

@keyframes width{
    from{
        width: 0%;
    }
    to{
        width: 100%;
    }
}

.second{
    z-index: -1;
}

.gradient(color="blue"){
    background-image: linear-gradient(45deg, #0136af, #22abfa);
}

.gradient(color="red"){
    background-image: linear-gradient(45deg, #d62926, #ee625f);
}

.gradient(color="green"){
    background-image: linear-gradient(45deg, #11998e, #1ce669);
}

.gradient(color="orange"){
    background-image: linear-gradient(45deg, #fc4a1a, #f7b733);
}

.gradient(color="black"){
    background-image: linear-gradient(45deg, #111, #666);
}

.logo{
    position: absolute;
    width: 100px;
    left: 20px;
    top: 20px;
}

.share{
    position: absolute;
    top: 15px;
    right: 15px;
    background-color: #fff;
    width: 50px;
    height: 50px;
    border-radius: 50%;
    text-align: center;
    font-size: 1.3rem;
    text-decoration: none;
    color: var(--primary);
    transition: .5s;
}

.share:hover{
    transform: scale(1.1);
}

.share i{
    line-height: 50px;
}

.nike{
    position: absolute;
    top: 85px;
    left: 15px;
    font-size: 11rem;
    text-transform: uppercase;
    line-height: .9;
    color: #fff;
    opacity: .1;
}

.shoe{
    position: absolute;
    width: 140%;
    opacity: 0;
    bottom: 0;
    right: 0;
    transform: rotate(-20deg);
    transition: .5s;
}

.shoe.show{
    opacity: 1;
}

.info{
    width: 50%;
    background-color: #fff;
    z-index: 1;
    padding: 35px 40px;
    box-shadow: 15px 0 35px rgba(0, 0, 0, 0.1),
    0 -15px 35px rgba(0, 0, 0, 0.1),
    0 15px 35px rgba(0, 0, 0, 0.1);
}

.shoeName{
    padding: 0 0 10px 0;
}

.shoeName div{
    display: flex;
    align-items: center;
}

.shoeName div .big{
    margin-right: 10px;
    font-size: 2rem;
    color: #333;
    line-height: 1;
}

.shoeName div .new{
    background-color: var(--primary);
    text-transform: uppercase;
    color: #fff;
    padding: 3px 10px;
    border-radius: 5px;
    transition: .5s;
}

.shoeName .small{
    font-weight: 500;
    color: #444;
    margin-top: 3px;
    text-transform: capitalize;
}

.shoeName, .description, .color-container, .size-container{
    border-bottom: 1px solid #dadada;
}

.description{
    padding: 10px 0;
}

.title{
    color: #3a3a3a;
    font-weight: 600;
    font-size: 1.2rem;
    text-transform: uppercase;
}

.text{
    color: #555;
    font-size: 17px;
}

.color-container{
    padding: 10px 0;
}

.colors{
    padding: 8px 0;
    display: flex;
    align-items: center;
}

.color{
    width: 25px;
    height: 25px;
    border-radius: 50%;
    margin: 0 10px;
    border: 5px solid;
    cursor: pointer;
    transition: .5s;
}

.color(color="blue"){
    background-color: #2175f5;
    border-color: #2175f5;
}

.color(color="red"){
    background-color: #f84848;
    border-color: #f84848;
}

.color(color="green"){
    background-color: #29b864;
    border-color: #29b864;
}

.color(color="orange"){
    background-color: #ff5521;
    border-color: #ff5521;
}

.color(color="black"){
    background-color: #444;
    border-color: #444;
}

.color.active{
    border-color: #fff;
    box-shadow: 0 0 10px .5px rgba(0, 0, 0, 0.2);
    transform: scale(1.1);
}

.size-container{
    padding: 10px 0;
    margin-bottom: 10px;
}

.sizes{
    padding: 8px 0;
    display: flex;
    align-items: center;
}

.size{
    width: 40px;
    height: 40px;
    border-radius: 6px;
    background-color: #eee;
    margin: 0 10px;
    text-align: center;
    line-height: 40px;
    font-size: 1.1rem;
    font-weight: 500;
    cursor: pointer;
    transition: .3s;
}

.size.active{
    background-color: var(--primary);
    color: #fff;
    transition: .5s;
}

.buy-price{
    padding-top: 15px;
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.price{
    color: #333;
    display: flex;
    align-items: flex-start;
}

.price h1{
    font-size: 2.1rem;
    font-weight: 600;
    line-height: 1;
}

.price i{
    font-size: 1.4rem;
    margin-right: 1px;
}

.buy{
    padding: .7rem 1rem;
    background-color: var(--primary);
    text-decoration: none;
    color: #fff;
    text-transform: uppercase;
    letter-spacing: 1px;
    font-weight: 500;
    font-size: 1.1rem;
    transition: .5s;
}

.buy:hover{
    transform: scale(1.1);
}

.buy i{
    margin-right: 2px;
}

@media (max-width: 1070px){
    .shoe{
        width: 135%;
    }
}

@media (max-width: 1000px){
    .card{
        flex-direction: column;
        width: 100%;
        box-shadow: 0 0 35px 1px rgba(0, 0, 0, 0.2);
    }
    
    .card > div{
        width: 100%;
        box-shadow: none;
    }

    .shoe{
        width: 100%;
        transform: rotate(-5deg) translateY(-50%);
        top: 55%;
        right: 2%;
    }

    .nike{
        top: 20%;
        left: 5%;
    }
}

@media (max-width: 600px){
    .share{
        width: 40px;
        height: 40px;
    }

    .share i {
        font-size: 1rem;
        line-height: 40px;
    }

    .logo{
        width: 70px;
    }
}

@media (max-width: 490px){
    .nike{
        font-size: 7rem;
    }

    .shoeName div .big{
        font-size: 1.3rem;
    }

    .small{
        font-size: 1rem;
    }

    .new{
        padding: 2px 6px;
        font-size: .9rem;
    }

    .title{
        font-size: .9rem;
    }

    .text{
        font-size: .8rem;
    }

    .buy{
        padding: .5rem .8rem;
        font-size: .8rem;
    }

    .price h1{
        font-size: 1.5rem;
    }

    .price i{
        font-size: .9rem;
    }

    .size{
        width: 30px;
        height: 30px;
        margin: 0 8px;
        font-size: .9rem;
        line-height: 30px;
    }

    .color{
        margin: 0 6px;
        width: 0 20px;
        width: 20px;
        height: 20px;
        border-width: 4px;
    }

    .share{
        width: 35px;
        height: 35px;
        top: 10px;
        right: 10px;
    }

    .share i{
        font-size: .8rem;
        line-height: 35px;
    }

    .logo{
        width: 60px;
        top: 10px;
        left: 10px;
    }

    .info{
        padding: 20px;
    }
}

@media (max-width: 400px){
    .buy i{
        display: none;
    }

    .container{
        padding: 20px;
    }
}```