JSFiddle - React, Tailwind, and code Playground

HTML

<div id="headContainer">

        <div id="blackBar">
            <div class="content">
                <img src="../Images/logo.png" class="logo" alt="logo" />
                <div id="clientSettings">
                    <div id="settingsContainer">
                        <ul>
                            <li><asp:LinkButton ID="endSession" OnClick="endSession_Click" Text="Exit" runat="server" /></li>
                            <li>not available</li>
                        </ul>
                    </div>
                </div>
                <div id="clientProfile"></div>
            </div>
        </div>


        <div id="grayBar">

        </div>

    </div>

CSS

#headContainer 
{
    top                 : 0;
    left                : 0;
    width               : 100%;
    height              : 100px;
    position            : fixed;
    z-index             : 1;
}

#headContainer div#grayBar
{
    top                 : 0;
    left                : 0;
    position            : relative;
    width               : 100%;
    height              : 50px;
    background-color    : #f1f1f1;
    z-index             : 1;
}
#clientSettings
{
    
    position            : relative;
    width               : 25px;
    height              : 50px;
    background-image    : url('../Images/Icons/endSession.png');
    background-repeat   : no-repeat;
    background-position : center center;
    z-index: 3;
}

#clientSettings:hover 
{
    cursor              : pointer;
    background-color    : #636363;  
}

#settingsContainer
{  
    position            : relative;
    top                 : 50px;
    left                : 0;
    padding             : 50px;
    background-color    : Green;
    z-index             : 2;
}

JavaScript

$(document).ready(function () {
                $('#clientSettings').click(function () {
                    $('#settingsContainer').toggle();
                });
            });