I have read in this site about a minor but annoying problem, a small gap before the actual content of my web page begins, but none of the solutions have worked for me. I have set all elements with 0 padding and 0 margin by default, but still something might be causing overflow.
This is my css file:
*{
    box-sizing: border-box;
    margin:0px;
    padding:0px;
    font-family: sans-serif;
}
//some global variables here
body{
    background-color: var(--brand-white);
    color:var(--brand-light-gray);
}
.header-landing{
    align-items: center;
    justify-content: space-between;
    padding:0 10px 0 10px;
    margin:15px 10px 0 10px;
}
.header-nav{
    display: flex;
    justify-content: center;
}
.header-nav > li{
    display:inline;
    list-style: none;
    padding:0 10px 0 10px; 
}
.header-logo{
    display: inherit;
    justify-content: center;
}
.main-content{
    background-color: var(--brand-light-gray-2);
    width: 100%;
}
the html file:
<!doctype html>
<html lang="es">
<head>
  <meta charset="utf-8">
  <title>nomihub</title>
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <link rel="stylesheet" type="text/css" href="style.css">
  <link rel="icon" type="image/x-icon" href="favicon.ico">
</head>
<body>
    <section class="main-content">
    <div class="header-landing flex-grid">
        <picture class="header-logo col-2">
            <h2>LOGO</h2>
        </picture>
        <div class="col-8">
            <ul class="header-nav">
                <li><a href="">Características</a></li>
                <li><a href="">Precio</a></li>
                <li><a href="">Partners</a></li>
                <li><a href="">Recursos</a></li>
            </ul>
        </div>
        <div class="col-2">
            <button class="btn-default">
                INGRESAR
            </button>
        </div>
    </div>
        <div class="main-content-welcome">
            <div class="welcome-header">
                <ul class="welcome-header__list">
                <li><h2>Bienvenidos</h2></li>
                <li><h1>El software de nomina más simple de todos</h1></li>
                <li><p>Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book.</p></li>
                 <li><button class="btn-default">
                        ACTIVAR DEMO
                     </button></li>
                </ul>    
            </div>
             <div class="main-content-features">
            <div class="welcome-container  ">
                <div class="circle"></div>
              <h3>ENCRIPTACIÓN</h3>  
                <p>Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s.</p>
              </div>
            <div class="welcome-container ">
                <div class="circle"></div>
               <h3>VIGILANCIA</h3>
                 <p>Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book.</p>
              </div>
            <div class="welcome-container ">
                <div class="circle"></div>
               <h3>RESPALDO</h3>
                 <p>Lorem Ipsum is simply dummy text of the printing and typesetting industry.</p>
              </div>
            <div class="welcome-container  ">
                <div class="circle"></div>
               <h3>LIMITES ESTRICTOS</h3>
                 <p>Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s.</p>
              </div>
        </div>
        </div>
    </section>
</body>
</html>
inspecting the elements with firefox, the white is before the actual body. How I get rid of this gap?