Hover on CSS is not working for my navigation bar

Question

I am messing around with web development, I have fallen into an issue with the hover section of CSS i cant get it to work on my site.

I did have this working when i had the navigation going vertical but then decided to have it horizontal instead which is where the issues started.

I have searched this on StackOverflow and have checked google but non of the solutions seem to help. Sorry if my code is a bit messy i will show you the sections that you need from the HTML and the CSS

HTML

<div id="nav">
    <ul>
            <li><a href="Home.html"><b><font size="5">Home</font></b></a></li>
            <li><a href="About.html"><b><font size="5">About</font></b></a></li>
            <li><a href="ContactUs.html"><b><font size="5">Contact Us</font></b></a></li>
    </ul>
</div>

CSS

#nav {
    /*width: 200px;*/
}

ul {
    list-style-type: none;
    margin: 0;
    padding: 0;
    overflow: hidden;
    background: linear-gradient(to bottom, white 10%, #2E3E9F 90%);
}

li{
    float: left;
}

li a{
    display: block;
    background-color: white;
    text-align: center;
    color: grey;
    padding: 14px 16px;
    text-decoration: none;
    border: 1px solid black;
}

li a:hover{
    background-color: grey;
    color: white;
}

Answer 1

Try this, its not great to use !important though. (Chrome)

  #nav { /*width: 200px;*/ } ul { list-style-type: none; margin: 0; padding: 0; overflow: hidden; background: linear-gradient(to bottom, white 10%, #2E3E9F 90%); } li { float: left; } li a { display: block; background-color: white; text-align: center; color: grey; padding: 14px 16px; text-decoration: none; border: 1px solid black; } li a:hover { background-color: grey !important; color: white !important; 

 <div id="nav"> <ul> <li><a href="Home.html"><b><font size="5">Home</font></b></a></li> <li><a href="About.html"><b><font size="5">About</font></b></a></li> <li><a href="ContactUs.html"><b><font size="5">Contact Us</font></b></a></li> </ul> </div>