How to apply the themes dynamically by selecting the theme from the dropdownlist in Asp.net MVC4?

Not the exact solution but still it's worth to look:
ASP.NET MVC Dynamic Themes[^]
You can customize the code as per your need.

And apart from this, you can do it using jQuery. Create the different .css files for each theme and based on the selection, load the theme for the page.
See,

$(".changeStyle").click(function (e) {
    e.preventDefault();
    var style = $(this).attr("data-style");
    $("#siteStyle").attr("href", style);
    localStorage.setItem("selected-skin", style);

});

// load selected color skin
if (localStorage.getItem("furnitureshop-skin"))
{
    $("#siteStyle").attr("href", localStorage.getItem("selected-skin"));
}

HTML:

<div class="panel-body">
             <label>Select the color theme</label>
             <ul class="skin-colors">
                 <li>
                     <a href="#" class="changeStyle" style="background-color: rgba(125, 63, 10, 1)" data-style="/Content/Site.css"></a>
                 </li>
                 <li>
                     <a href="#" class="changeStyle" style="background-color:#000" data-style="/Content/Black-Skin.css"></a>
                     </li>
                 <li>
                     <a href="#" class="changeStyle" style="background-color: #8C489F" data-style="/Content/Purple-Skin.css"></a>
                 </li>
                 <li>
                     <a href="#" class="changeStyle" style="background-color: #DF3232" data-style="/Content/Red-Skin.css"></a>
                 </li>
             </ul>
         </div>

-KR