How can I get bookmarked hash links to work with a jQuery change function?

What's the simplest way with this jQuery change function to enable bookmarked hash links to work, i.e to be able to use example.com/#theme1 or example.com/#theme2 links?

The jQuery #theme-selector changes the hash and shows/hides the relevant divs with the class, i.e. .theme1 or .theme2, but when going to example.com/#theme1 from a bookmarked link, all divs are shown.

In addition, if I refresh example.com/#theme1, the hash remains #theme1, but all divs are shown.

Some other questions on SO deal with bookmarkable hashes, but they're many years old. And some libraries that appear useful are ten years old, too, like https://github.com/asual/jquery-address

Unfortunately, running the snippet here won't show browser hash changes, nor will JSFiddle.

Any ideas?

  jQuery(document).ready(function(jQuery){
    
        jQuery("#theme-selector").change(function () {
    
        var urlhash = document.getElementById('theme-selector').value;
    
        window.location.hash = urlhash;
    
    });
    
    
    jQuery("#theme-selector").change(function () {
    
    themeclass = window.location.hash.substr(1);
    
    jQuery('.blockcontent').hide();
    jQuery('.' +themeclass).show();
    jQuery('.theme-header').hide();
    jQuery('.' +themeclass).show();
    
        });
    
    });

 .blockcontent {
    display:inline-block;
    width:150px;
    border:1px solid #acacac;
    }
    
    .theme-header {
    display:none;
    }

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>

 <label for="theme-selector">Filter by Theme:</label>
    
    <select name="theme-selector" id="theme-selector" value="">
    
    <option value="all-themes">All Themes</option>
    <option value="theme1">Theme 1</option>
    <option value="theme2">Theme 2</option>
    <option value="theme3">Theme 3</option>
    
    </select>
    
    <br>
    
    <div id="theme-description-container">
    <div class="theme1 theme-header">Theme 1 Description</div>
    <div class="theme2 theme-header">Theme 2 Description</div>
    <div class="theme3 theme-header">Theme 3 Description</div>
    </div>
   
    <br>
    
    <div class="blockcontent all-themes theme1">
    theme1<br><br>Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do 
    </div>
    
    <div class="blockcontent all-themes theme2">
    theme2<br><br>sed do eiusmod tempor incididunt sed do eiusmod eiusmod
    </div>
    
    <div class="blockcontent all-themes theme3 theme2">
    theme2 and theme3<br><br>consectetur adipiscing elit,consect adipiscing elit, 
    </div>
    
    <div class="blockcontent all-themes theme3">
    theme3<br><br>consectetur adipiscing elit,consect etur adipiscing elit, 
    </div>

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