JSFiddle - React, Tailwind, and code Playground

HTML

<div class="a">
    <div>
        <ul class="b">
            <li class="c">
                <input id="123" type="checkbox" checked></input>
                <label for="123">test</label>
            </li>
            <li class="c">
                <input id="456" type="checkbox"></input>
                <label for="456">test</label>
            </li>
        </ul>
    </div>
</div>

CSS

.a {
    text-decoration: line-through;
}

.a .b .c input[type="checkbox"]:not(:checked) + label {
	text-decoration: none !important;
}