prog/html/style.css

body {
    margin: 0;
}
.header-fixed {
    position: fixed;
    top: 0;
    z-index: 1;
    width: 100%;
}

.navbar {
    display: flex;
    line-height: 60px;
}

.navbar .logo {
    flex: 3;
}

.navbar nav {
    flex: 8;
}

.navbar label {
    user-select: none;
    cursor: pointer;
    padding: 28px 20px;
    position: relative;
    z-index: 3;
}

.navbar label i {
    height: 2px;
    position: relative;
    transition: background .2s ease-out;
    width: 18px;
    font-style: normal;
    font-weight: normal;
}
.navbar label i:before,
.navbar label i:after {
    content: '';
    height: 100%;
    position: absolute;
    transition: all .2s ease-out;
    width: 100%;
}
.navbar label i,
.navbar label i:before,
.navbar label i:after {
    display: block;
    background:black;
}
.navbar label i:before {
    top: 5px;
}
.navbar label i:after {
    top: -5px;
}

.navbar #navbar-toggle {
    display: none;
}

.header #navbar-toggle:checked ~ .menu {
    visibility: visible;
    opacity: 0.99;
}
.header #navbar-toggle:checked ~ label {
    background: #212121;
    border-radius: 50%;
}
.header #navbar-toggle:checked ~ label i {
    background: transparent;
}
.header #navbar-toggle:checked ~ label i:before {
    transform: rotate(-45deg);
}
.header #navbar-toggle:checked ~ label i:after {
    transform: rotate(45deg);
}
.header #navbar-toggle:checked ~ label:not(.steps) i:before,
.header #navbar-toggle:checked ~ label:not(.steps) i:after {
    top: 0;
}

@media (max-width: 768px) {
    .navbar nav {
        visibility: hidden;
        opacity: 0;
        position: fixed;
        top: 0px;
        left: 0px;
        width: 100%;
        height: 100%;
        transition: all 0.3s ease-out;
        display: table;
        background: #ddd;
    }
    .navbar nav ul {
        margin: 0;
        padding: 20px 0;
        display: table-cell;
        vertical-align: middle;
    }
    .navbar nav li {
        display: block;
        padding: 20px 0;
        text-align: center;
        font-size: 50px;
        min-height: 50px;
        font-weight: bold;
        cursor: pointer;
        transition: all 0.3s ease-out;
    }
}

@media (min-width: 768px) {
    .navbar nav ul {
        margin: 0;
        padding: 0;
        display: flex;
        justify-content: space-around;
        text-align: center;
        list-style: none;
    }
    .navbar nav li {
        flex: 1;
    }
    .navbar nav li a {
        display: block;
        padding: 0 8px;
        line-height: 60px;
    }
    .navbar label {
        display: none;
    }
}