JSFiddle - React, Tailwind, and code Playground

HTML

<body id="body">
    <input type="button" class="changeBg" onclick="day();" value="Day" />
    <input type="button" class="changeBg" onclick="night();" value="Night" />
    <input type="button" class="changeBg" onclick="reset();" value="Reset" />
</body>

CSS

.darkSwitch {
    background: #808080;
}
.lightSwitch {
    background: #ffff99;
}

JavaScript

function day() {
    body.className = "lightSwitch";
};

function night() {
    body.className = "darkSwitch";
};

function reset() {
    body.className = "";
};

$(function () {
    var bgColor = document.cookie.replace(/(?:(?:^|.*;\s*)bgColor\s*\=\s*([^;]*).*$)|^.*$/, "$1");
    
    var button = $('input[type=button].changeBg');
    button.on('click', function (event) {
        event.preventDefault();
        
        eval($(this).val().toLowerCase() + "();");

        button.not($(this)).removeAttr('disabled');
        if ($(this).val() != "Reset") {
            $(this).attr('disabled', '');
            document.cookie = "bgColor="+$(this).val();
        }
    });

    if(bgColor.length > 0)
    {     
        eval(bgColor.toLowerCase()+'()'); 
        $.each($('input[type="button"].changeBg'),function(){
            if($(this).val() == bgColor)
                $(this).attr('disabled','disabled');
        });
    }
});