已更新

使用headbannerin类添加了额外的cover div，将其与.dropdown的父类分开，因此现在我们可以分别使用z-index。 并更改了#financechoice中的z-index:3

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body {
    background-color: #F2F2F2;
    background-size: cover;
}

.headBanner {
    height: 10vh;
    width: 100%;
    clear: top;
    position: fixed;
    z-index: 100;
}

/* added the, with z-index: 2 */
.headBannerIn {
    height: 100%;
    width: 100%;
    background-color: #007AFF;
    position: absolute;
    z-index: 2;
}

.dropdown-content {
    visibility: hidden;
  display: block;
  position: relative;
  background-color: #8FC4FF;
  min-width: 160px;
  z-index: 1;
  top: 100%;
  width: 100%;
  height: 30vh;
  box-shadow: 0px 8px 16px 0px rgba(0,0,0,0.2);
    padding: 12px 16px;
    opacity: 0;
}

.dropdown:hover .dropdown-content {
    display: block;
    animation: bannerFadeIn 1s linear forwards;
    visibility: visible;
    opacity: 1;
    z-index: -1;
    position: absolute;
    top: 100%;
}

@keyframes bannerFadeIn {
  from {
    opacity: 0;

    transform: translateY(-300px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

#innerSpace1 {
    position: absolute;
    height: 80%;
    width: 17.25%;
    background-color: transparent;
    top: 10%;
    left: 14%;
    border-right: 3px solid;

}

#innerSpace2 {
    position: absolute;
    height: 80%;
    width: 13%;
    left: 31.5%;
    background-color: transparent;
    top: 10%;
    border-right: 3px solid;
}

#innerSpace3 {
    position: absolute;
    height: 80%;
    width: 15%;
    left: 44.9%;
    background-color: transparent;
    top: 10%;
}

#innerSpace4 {
    position: absolute;
    height: 100%;
    width: 20%;
    left: 59.25%;
    background-color: transparent;
    top: 0%;
}

#coursesHead {
    position: absolute;
    font-family: 'Roboto';font-size: 2vw; color: white;
    top: 6%;
    left: 27%;
    text-decoration: underline;
}

#coursesList {
    position: absolute;
    font-family: 'Roboto';font-size: 1vw; color: white;
    top: 28%;
    left: 29%;
    font-weight: bold;
    line-height: 170%;
    cursor: pointer;
}

#toolsHead {
    text-align: center;
    position: absolute;
    font-family: 'Roboto';font-size: 2vw; color: white;
    width: 60%;
    height: 30%;
    top: 50%;
    left: 50%;
    margin-left: -30%;
    margin-top: -15%;
    cursor: pointer;
}

#articlesHead {
    position: absolute;
    font-family: 'Roboto';font-size: 2vw; color: white;
    top: 6%;
    left: 30%;
    text-decoration: underline;
}

* {
    padding: 0;
    margin: 0;
}

#logo {
    bottom: 10%;
    top: 10%;
    width: 4%;
    left: 20%;
    height: 80%;
    position: absolute;
    background-image: url("blue logo.png");
    background-position: center; /* Center the image */
    background-repeat: no-repeat; /* Do not repeat the image */
    background-size: cover;
    display: inline-block;
}

#financeChoice {
    width: 9.8%;
    height: 10vh;
    top: 0%;
    bottom: 0%;
    left: 24.8%;
    display: inline-block;
    position: relative;
    font-family: 'Roboto';font-size: 2vw; color: white;
    background-color: transparent;
    border: none;
    z-index: 3; /* changed form 2 to 3, so it fill be over the menu */
    cursor: pointer;
}

#choice2 {
    width: 9.8%;
    height: 90%;
    top: 5%;
    bottom: 5%;
    left: 34.8%;
    display: inline-block;
    position: absolute;
    font-family: 'Roboto';font-size: 2vw; color: white;
    background-color: transparent;
    border: none;
}

#choice3 {
    width: 9.8%;
    height: 90%;
    top: 5%;
    bottom: 5%;
    left: 44.8%;
    display: inline-block;
    position: absolute;
    font-family: 'Roboto';font-size: 2vw; color: white;
    background-color: transparent;
    border: none;
}

#choice4 {
    width: 9.8%;
    height: 90%;
    top: 5%;
    bottom: 5%;
    left: 54.8%;
    display: inline-block;
    position: absolute;
    font-family: 'Roboto';font-size: 1.7vw; color: white;
    background-color: transparent;
    border: none;
}

#choice5 {
    width: 9.8%;
    height: 90%;
    top: 5%;
    bottom: 5%;
    left: 64.8%;
    display: inline-block;
    position: absolute;
    font-family: 'Roboto';font-size: 1.7vw; color: white;
    background-color: transparent;
    border: none;
}

#loginButton {
    width: 5vh;
    height: 5vh;
    top: 20%;
    bottom: 20%;
    left: 75%;
    display: inline-block;
    position: absolute;
    background-image: url("google login.jpg");
    background-position: center; /* Center the image */
    background-repeat: no-repeat; /* Do not repeat the image */
    background-size: cover;
    border-radius: 50%;
}

#tab1 {
    width: 4.9%;
    height: 10%;
    top: 90%;
    left: 27.25%;
    display: inline-block;
    position: absolute;
    background-color: #1DBF2D;
    z-index: 0;
}

#tab2 {
    width: 4.9%;
    height: 10%;
    top: 90%;
    left: 37.25%;
    display: inline-block;
    position: absolute;
    background-color: #1DBF2D;
}

#tab3 {
    width: 4.9%;
    height: 10%;
    top: 90%;
    left: 47.25%;
    display: inline-block;
    position: absolute;
    background-color: #1DBF2D;
}

#tab4 {
    width: 4.9%;
    height: 10%;
    top: 90%;
    left: 57.25%;
    display: inline-block;
    position: absolute;
    background-color: #1DBF2D;
}

#tab5 {
    width: 4.9%;
    height: 10%;
    top: 90%;
    left: 67.25%;
    display: inline-block;
    position: absolute;
    background-color: #1DBF2D;
}

<!DOCTYPE html>
<html lang="en">
    <title>
        Welcome Page
        <meta charset="utf-8">
        <meta name="viewport" content="width=device-width, initial-scale=1">
    </title>
    <body>
        <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.5.1/jquery.min.js"></script>
        <link rel="stylesheet" href="C:\Users\rzemi\OneDrive\Desktop\web\cssPages\WelcomeStyle.css">
        <link rel="stylesheet" href="C:\Users\rzemi\OneDrive\Desktop\web\cssPages\banner.css">
        <div class="headBanner" id="headBanner">
      <!-- added extra cover -->
      <div class="headBannerIn">
        <div id="logo" onclick="location.href = 'Welcome.html';"></div>
        <button type="button" id="choice2" onclick="location.href = 'InvestingHome.html';">Investing</button>
        <button type="button" id="choice3" onclick="location.href = 'EarlyStartHome.html';">Early Start</button>
        <button type="button" id="choice4" onclick="location.href = 'RetirementHome.html';">Retirement</button>
        <button type="button" id="choice5">Community</button>
        <div id="tab1"></div>
        <div id="tab2"></div>
        <div id="tab3"></div>
        <div id="tab4"></div>
        <div id="tab5"></div>
        <button type="button" id="loginButton"></button>
      </div>
            <div class="dropdown" id="dropdown">
                <button class="dropbtn" type="button" id="financeChoice" onclick="location.href = 'FinancesHome.html';">
                    Finance
                    <i class="fa fa-caret-down"></i>
                </button>
                <div class="dropdown-content">
                    <div id="topDropdown">
                        <div class="innerSpace" id="innerSpace1">
                            <h2 id="coursesHead">Courses</h2>
                            <ol id="coursesList">
                                <li onclick="location.href = 'Finances-intro1-Course.html';">Introduction</li>
                                <li onclick="location.href = 'Finances-TandP1-Course.html';">Tracking And Planning</li>
                                <li onclick="location.href = 'Finances-CDB1-Course.html';">Credit, Debt and Banking</li>
                                <li onclick="location.href = 'Finances-Savings1-Course.html';">Saving</li>
                                <li onclick="location.href = 'Finances-Taxes1-Course.html';">Taxes</li>
                            </ol>
                        </div>
                        <div class="innerSpace" id="innerSpace2">
                            <h2 id="toolsHead" onclick="location.href = 'financeToolOverview.html';">Financial Tool</h2>
                        </div>
                        <div class="innerSpace" id="innerSpace3">
                            <h2 id="articlesHead">Articles</h2>
                        </div>
                    </div>
                </div>
            </div>
        </div>
        <div id="topWelcome">
            <div id="topWelcomeWriting">Hey guys, you ready to get you're finincial freedom on its way? <br>...</div>
            <div id="topSemi"></div>
            <div id="bottomSemi"></div>
        </div>
    </body>
</html>