index.css

body{
    background-color: #f1f1f1;
    margin: 0%;
    top:0;
}

.nav-main{
    width: 100%;
    height: 60px;
    background-color: #fff;
    display: flex;
    flex-wrap: wrap;
    z-index: 1000;
    position: fixed;
    top: 0;
    margin: 0;
}

.nav-main ul{
    display: flex;
    flex-wrap: wrap;
    padding-left: 15px;
}

.nav-main ul li{
    list-style: none;
}

.nav-main ul a{
    display: block;
    height: 100%;
    padding: 0 10px;
    text-transform: uppercase;
    text-decoration: none;
    color: navy;
    font-family: sans-serif;
    font-size: 20px;
    transition: all 0.4s ease-in-out;
}

.nav-main ul a:hover{
    font-size: 23px;
}

.btn-toggle-nav{
    width: 60px;
    height: 100%;
    background-color: aqua;
    background-image: url(thumb-1920-949023.jpg);
    background-repeat: no-repeat;
    background-size: 125%;
    background-position: center;
    cursor: pointer;
    transition: all 0.3s;
}

.btn-toggle-nav:hover{
    opacity: 0.7;
}

.nav-sidebar{
    position: fixed;
    left:0;
    bottom: 0;
    margin-top: 60px;
    width: 50px;
    padding: 0 5px;
    height: 91.525vh;
    background-color: #1b1b1b;
    z-index: 1000;
    transition: all 0.4s ease-in-out;
}

.nav-sidebar ul{
    display: flex;
    flex-wrap: wrap;
    flex-direction: column;
    padding-top: 15px;
    overflow: hidden;
    visibility: hidden;
}

.nav-sidebar ul li{
    line-height: 60px;
    list-style: none;
}

.nav-sidebar ul li span{
    display: block;
    height: 60px;
    padding: 0 10px;
    text-decoration: none;
    text-transform: uppercase;
    color: #fff;
    font-family: sans-serif;
    font-size: 20px;
    white-space: nowrap;
    opacity: 0;
    transition: all 0.4s ease-in-out;
}

.nav-sidebar ul li span:hover{
    color: #222;
    background-color: #fff;
}