navbar responsive issue when resize the browser width?

Question

i have an issue for the responsive navbar, when i resize the browser for the mobile view and open then close the menu button, after that make the browser full screen for the big screen view the navbar will disappear any help for that issue

i need to add another feature to fix the navbar when scroll down but when scroll on the mobile the menu it looks messed up

below my code(on snippet)

$(document).ready(function(){
    $(".menu").click(function(){
        $("nav").slideToggle(800);
    })
});

nav{
    width: 100%;
    background: #202c45;
    padding: 0 50px;
    box-sizing: border-box;
}
nav h1{
    margin: 0;
    padding: 0;
    float: left;
    padding-top: 18px;
}

nav h1 a{
    color: #fff;
    text-decoration: none;    

}

nav ul{
    margin: 0;
    padding: 0;
    float: right;
}

nav ul li{
    list-style: none;
    display: inline-block;
    padding: 20px;
    transition: 0.5s;
    }

nav ul li:hover{
    background: #f2184f;
}

nav ul li a{
    color: #fff;
    text-decoration: none;
}

.responsive-bar{
    width: 100%;
    background: #202c45;
    padding: 10px 30px;
    box-sizing: border-box;
    display: none;
}

.responsive-bar h3{
    margin: 0;
    padding: 3px 0;
    float: left;
    color:#fff;
}
.responsive-bar h3 a{
    color:#fff;
    text-decoration: none;
    }
.responsive-bar h4{
    margin: 0;
    padding: 0;
    color: #fff;
    float: right;
    cursor: pointer;
    padding: 5px 10px;
    background:#f2184f;
    text-transform: uppercase;
}

@media (max-width:768px){
    nav{ 
        display: none;
        padding: 0;
    }
    .responsive-bar{
        display: block;
    }
    nav h1{
        display: block;
        float: none;
    }
    nav ul{
        float: none;
    }
    nav ul li{
        display: block;
        text-align: center;
        padding: 15px 20px;
        border-bottom: 1px solid rgba(255,255,255,.1)
    }
    #full-logo{
        display: none;
    }
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.0.0/jquery.min.js"></script>
<nav>
    <h1 id="full-logo"><a href="#">MyCar</a></h1>
    <ul>
        <li><a href="#">Home</a></li>
        <li><a href="#">About</a></li>

    </ul>
    <div style="clear:both;"></div>
</nav>
<div class="responsive-bar">
        <h3 class="brand"><a href="#">MyCar</a></h3>
    <h4 class="menu">Menu</h4>
    <div style="clear:both;"></div>

</div>

Answer 1

As per your html structure you have to add below code to your css

@media (min-width:768px){
    nav{
        display: block !important;
    }
}

Using this you don't have to make any changes in your html and css.

$(document).ready(function(){
    $(".menu").click(function(){
        $("nav").slideToggle(800);
    })
});

nav{
    width: 100%;
    background: #202c45;
    padding: 0 50px;
    box-sizing: border-box;
}
nav h1{
    margin: 0;
    padding: 0;
    float: left;
    padding-top: 18px;
}

nav h1 a{
    color: #fff;
    text-decoration: none;    

}

nav ul{
    margin: 0;
    padding: 0;
    float: right;
}

nav ul li{
    list-style: none;
    display: inline-block;
    padding: 20px;
    transition: 0.5s;
    }

nav ul li:hover{
    background: #f2184f;
}

nav ul li a{
    color: #fff;
    text-decoration: none;
}

.responsive-bar{
    width: 100%;
    background: #202c45;
    padding: 10px 30px;
    box-sizing: border-box;
    display: none;
}

.responsive-bar h3{
    margin: 0;
    padding: 3px 0;
    float: left;
    color:#fff;
}
.responsive-bar h3 a{
    color:#fff;
    text-decoration: none;
    }
.responsive-bar h4{
    margin: 0;
    padding: 0;
    color: #fff;
    float: right;
    cursor: pointer;
    padding: 5px 10px;
    background:#f2184f;
    text-transform: uppercase;
}

@media (max-width:768px){
    nav{ 
        display: none;
        padding: 0;
    }
    .responsive-bar{
        display: block;
    }
    nav h1{
        display: block;
        float: none;
    }
    nav ul{
        float: none;
    }
    nav ul li{
        display: block;
        text-align: center;
        padding: 15px 20px;
        border-bottom: 1px solid rgba(255,255,255,.1)
    }
    #full-logo{
        display: none;
    }
}
@media (min-width:768px){
	nav{
	    display: block !important;
	}
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.0.0/jquery.min.js"></script>
<nav>
    <h1 id="full-logo"><a href="#">MyCar</a></h1>
    <ul>
        <li><a href="#">Home</a></li>
        <li><a href="#">About</a></li>

    </ul>
    <div style="clear:both;"></div>
</nav>
<div class="responsive-bar">
        <h3 class="brand"><a href="#">MyCar</a></h3>
    <h4 class="menu">Menu</h4>
    <div style="clear:both;"></div>

</div>