flexbox demo

gistfile1.txt

<style>
  body {
    background-color: yellow;
    margin: 0;
  }

  .header-center {
    background-color: red;
    max-width: 1200px;
    height: 200px;
    margin: 0 auto;
    /* overflow: hidden; */
    display: flex;
    justify-content: space-between;
    align-items: center;
    flex-direction: row;
  }


  .header-center nav a {
    color: #fff;
    text-decoration: none;
    display: inline-block;
    padding: 20px;
  }

  @media screen and (max-width: 900px) {/* 0 - 900*/
    body {
        background-color: orange;
    }

    .header-center {
      flex-direction: column;
    }
  }

  @media screen and (max-width: 700px) { /* 0 - 700*/
    body {
        background-color: purple;
    }
  }

  /* .nav-left {
    float: left;
  }

  .nav-right {
    float: right;
  }  */
</style>
<header>
  <div class="header-center">
  
    <nav class="nav-left">
      <a href="">logo</a>
      <a href="">Cursos</a>
      <a href="">Comunidad</a>
    </nav>
    
    <nav class="nav-right">
      <a href="">Planes</a>
      <a href="">Ingresar</a>
      <a href="">Regístrate gratis</a>
    </nav>
    
  </div>
</header>