style.css

body, ul, li, p {
    margin: 0px;
    list-style: none;
    font-family: "lato", sans-serif;
}
#logo {
    margin-left: 1em;
    width: 30px;
    max-width: auto;
    padding: 0;
}

img {
    max-width: 100%;
}

.header {
    top: 0;
    width: 100%;
    position: fixed;
    background-color: grey;
    display: flex;
    flex-wrap: wrap;
    padding: 0;
    align-items: center;
    justify-content: space-between;
    
}
.menu {

    display: flex;
    flex-wrap: wrap;
    
}
.menu li {
    font-size: 0.7em;
    justify-content: space-between;
    display: block;
    padding: 11px;
    
}

menu li a {
    font-size: 0.2em;
    justify-content: space-between;
    display: block;
    
}
.sidebar {
    margin: 0;
    padding: 0;
    width: 200px;
    background-color: #f1f1f1;
    position: fixed;
    height: 100%;
    overflow: auto;
}
.sidebar a {
    display: block;
    color: black;
    padding: 10px;
    text-decoration: none;
}
.sidebar a.active {
    background-color: grey;
    color: white;
}

.sidebar a:hover:not(.active) {
    background-color: rgb(71, 69, 69);
    color: white;
}

div.content {
    margin-top: 35px;
    margin-left: 200px;
    padding: 1px 16px;
    height: 1000px;
}

@media screen and (max-width:700px) {
    .sidebar {
        width: 100%;
        height: auto;
        position: relative;
    }
    .sidebar a {float: left;}
    div.content {margin-left: 0;}
}
@media screen and (max-width:400px) {
    .sidebar a {
        text-align: center;
        float: none;
    }
}