Html 如何修复与导航栏重叠的css网格

我对html和css还是个新手.我不知道如何修复与我的粘性导航栏重叠的网格.我使用以下方法创建了栅格:

        <section id="projects">
            <h2>PROJECTS</h2>
            <div class="grid-container">
                <div class="grid-item">
                    <p><b>Project 1</b></p>
                    <img src="image1.png" alt="image1" class="image1>
                    <div class="overlay">
                        <div class="projects-text">
                            Placeholder
                            <br><a class="repo-text" href="">Repo Link</a> 
                        </div>
                    </div>
                </div>
                <div class="grid-item">
                    <p><b>Project 2</b></p>
                    <img src="image2.jpg" alt="image2" class="image2">
                    <div class="overlay">
                        <div class="projects-text">
                            Placeholder
                            <br><a class="repo-text" href="">Repo Link</a>
                        </div>
                    </div>
                </div>
                <div class="grid-item">
                    <p><b>Project 3</b></p>
                    <img src="image3.jpg" alt="image3" class="image3">
                    <div class="overlay">
                        <div class="projects-text">
                            Placeholder
                            <br><a class="repo-text" href="">Repo Link</a>
                        </div>
                    </div>
                </div>
            </div>
        </section>

并使用此css:

.grid-container {
    display: grid;
    grid-template-columns: auto auto auto;
    padding: 10px;
    grid-column-gap: 20px;
    grid-row-gap: 20px;
}

.grid-item {
    background-color: white;
    border: 5px solid lavender;
    border-radius: 15px;
    padding: 20px;
    font-size: 30px;
    text-align: center;
    justify-content: center;
    height: 350px;
    position: relative;
}

.overlay {
    position: absolute;
    top: 0;
    bottom: 0;
    left: 0;
    right: 0;
    height: 100%;
    width: 100%;
    opacity: 0;
    transition: .5s ease;
    background-color: lavender;
}

.grid-item:hover .overlay{
    opacity: 1;
}

这是我的导航栏:

        <nav>
            <ul>
                <li><a href=""></a></li>
                <li><a href=""></a></li>
                <li><a href=""></a></li>
                <li><a href=""></a></li>
                <li><a href=""></a></li>
            </ul>
        </nav>

nav {
    overflow: hidden;
    width: 100%;
}

nav ul {
    list-style-type: none;
    margin: 0;
    padding: 0;
    overflow: hidden;
    top: 0;
    width: 100%;
    position: fixed;
}

nav li {
    font-family: "";
    float: left;
}

nav a {
    display: block;
    text-align: center;
    padding: 14px 16px;
    text-decoration: none;
    position: relative;
}

nav a::after {
    content: "";
    display: block;
    position: absolute;
    left: 0;
    bottom: 0;
    width: 0;
    height: 5px;
    transition: width 0.3s ease;
}

nav a:hover::after {
    width: 100%;
}

在注释掉代码行之后，我意识到问题出在position:relativein.grid-Item上，但是如果我删除它或更改属性，覆盖效果就不再起作用了.我如何解决这个问题，或者有没有更好的方法来实现这个问题？