问标题与我的滚动条HTML/CSS重叠

EN

header {
    overflow: hidden;
    z-index: 100;
    position: fixed;
    width: 100%;
    top: 0;
    right: 0;
    left: 0;
    background-color: #fff
}
nav {
    float: right;
}

nav ul {
    margin: 0;
    padding: 2.8em 2em;
}

nav ul li {
    display: inline;
    padding: 0 .4em;
}

nav ul li a {
    color: #222222;
    text-decoration: none;
    font-size: 20px;
    padding-bottom: .5em;
    transition: .5s color;
}

nav ul li a:hover {
    border-bottom: 3px solid #222222;
}