Оригинальное зачеркивавшие checkbox'ов

 
<form>
    <label><input class="pristine" type="checkbox" name="A" checked> <span>Купить</span></label>
    <br>
    <label><input class="pristine" type="checkbox" name="B"> <span>Забрать</span></label>
    <br>
    <label><input class="pristine" type="checkbox" name="C"> <span>Принести</span></label>
    <br>
    <label><input class="pristine" type="checkbox" name="D"> <span>Собрать</span></label>
</form>

 
document.addEventListener("DOMContentLoaded",function(){
    this.forms[0].addEventListener("change",e => {
        e.target.removeAttribute("class");
    });
});

 
* {
    border: 0;
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}
:root {
    --bg: #e3e4e8;
    --checkBg: #ffffff;
    --checkBorder: #c7cad1;
    --fg: #17181c;
    --fgDim: #5c6270;
    --primary: #255ff4;
    --dur: 0.6s;
    font-size: calc(16px + (24 - 16) * (100vw - 320px) / (1280 - 320));
}
body, input {
    color: var(--fg);
    font: 1em/1.5 system-ui, -apple-system, sans-serif;
}
body {
    background: var(--bg);
    display: grid;
    height: 100vh;
    place-items: center;
}
label, input[type=checkbox] {
    cursor: pointer;
}
label {
    display: inline-flex;
    align-items: center;
    margin-bottom: 0.75em;
    position: relative;
    -webkit-tap-highlight-color: transparent;
}
input[type=checkbox], input[type=checkbox]:before, input[type=checkbox]:after {
    width: 1.5rem;
    height: 1.5rem;
}
input[type=checkbox], input[type=checkbox]:before {
    background: var(--checkBg);
    border-radius: 0.2em;
    box-shadow: 0 0 0 1px var(--checkBorder) inset;
}
input[type=checkbox]:before, input[type=checkbox]:after {
    display: block;
    position: absolute;
    top: 0;
    left: 0;
}
input[type=checkbox] {
    margin-right: 0.75em;
    -webkit-appearance: none;
    appearance: none;
}
input[type=checkbox] + span {
    animation: brighten var(--dur) linear;
}
input[type=checkbox]:before {
    animation: unstrike var(--dur) linear;
    content: "";
    transform-origin: 0 50%;
    z-index: 1;
}
input[type=checkbox]:after {
    color: var(--primary);
    content: "\2713";
    font-size: 1.5em;
    line-height: 1;
    text-align: center;
}
input[type=checkbox]:focus {
    outline: transparent;
}
input[type=checkbox]:focus + span {
    text-decoration: underline;
}
input[type=checkbox]:checked + span {
    animation-name: dim;
    color: var(--fgDim);
}
input[type=checkbox]:checked:before {
    animation-name: strike;
    background: var(--fgDim);
    border-radius: 0;
    box-shadow: 0 0 0 1px var(--fgDim) inset;
    transform: translateX(2.25em) scale(1,0.05);
    width: calc(100% - 2.25em);
}
input[type=checkbox].pristine:before, input[type=checkbox].pristine + span {
    animation: none;
}
/* Dark mode */
@media (prefers-color-scheme: dark) {
    :root {
        --bg: #17181c;
        --checkBg: #2e3138;
        --checkBorder: #454954;
        --fg: #e3e4e8;
        --fgDim: #8f95a3;
        --primary: #5583f6;
    }
}
/* Animations */
@keyframes dim {
    from, 83% {
        color: var(--fg);
    }
    to {
        color: var(--fgDim);
    }
}
@keyframes brighten {
    from {
        color: var(--fgDim);
    }
    17%, to {
        color: var(--fg);
    }
}
@keyframes unstrike {
    from {
        background: var(--fgDim);
        border-radius: 0;
        box-shadow: 0 0 0 1px var(--fgDim) inset;
        transform: translateX(2.25em) scale(1,0.05);
        width: calc(100% - 2.25em);
    }
    14% {
        background: var(--fg);
        border-radius: 0;
        box-shadow: 0 0 0 1px var(--fg) inset;
        transform: translateX(2.25em) scale(1,0.05);
        width: calc(100% - 2.25em);
    }
    29% {
        background: var(--fg);
        border-radius: 0;
        box-shadow: 0 0 0 1px var(--fg) inset;
        transform: translateX(2.75em) scale(1,0.05);
        width: calc(100% - 2.25em);
    }
    43% {
        background: var(--fg);
        border-radius: 0;
        box-shadow: 0 0 0 1px var(--fg) inset;
        transform: translateX(-0.5em) scale(0.75,0.05);
        width: 1.5em;
    }
    57% {
        background: var(--fg);
        border-radius: 0;
        box-shadow: 0 0 0 1px var(--fg) inset;
        transform: translateX(0) scale(1,0.05);
        width: 1.5em;
    }
    71% {
        background: var(--fg);
        border-radius: 0.2em;
        box-shadow: 0 0 0 1px var(--fg) inset;
        transform: translateX(0) scale(1,1.25);
        width: 1.5em;
    }
    86% {
        background: var(--fg);
        border-radius: 0.2em;
        box-shadow: 0 0 0 1px var(--fg) inset;
        transform: translateX(0) scale(1,1);
        width: 1.5em;
    }
    to {
        background: var(--checkBg);
        border-radius: 0.2em;
        box-shadow: 0 0 0 1px var(--checkBorder) inset;
        transform: translateX(0) scale(1,1);
        width: 1.5em;
    }
}
@keyframes strike {
    from {
        background: var(--checkBg);
        border-radius: 0.2em;
        box-shadow: 0 0 0 1px var(--checkBorder) inset;
        transform: translateX(0) scale(1,1);
        width: 1.5em;
    }
    17% {
        background: var(--fg);
        border-radius: 0.2em;
        box-shadow: 0 0 0 1px var(--fg) inset;
        transform: translateX(0) scale(1,1);
        width: 1.5em;
    }
    33% {
        background: var(--fg);
        border-radius: 0;
        box-shadow: 0 0 0 1px var(--fg) inset;
        transform: translateX(0) scale(1,0.05);
        width: 1.5em;
    }
    50% {
        background: var(--fg);
        border-radius: 0;
        box-shadow: 0 0 0 1px var(--fg) inset;
        transform: translateX(-0.5em) scale(1,0.05);
        width: 1.5em;
    }
    67% {
        background: var(--fg);
        border-radius: 0;
        box-shadow: 0 0 0 1px var(--fg) inset;
        transform: translateX(2.25em) scale(1.25,0.05);
        width: calc(100% - 2.25em);
    }
    83% {
        background: var(--fg);
        border-radius: 0;
        box-shadow: 0 0 0 1px var(--fg) inset;
        transform: translateX(2.25em) scale(1,0.05);
        width: calc(100% - 2.25em);
    }
    to {
        background: var(--fgDim);
        border-radius: 0;
        box-shadow: 0 0 0 1px var(--fgDim) inset;
        transform: translateX(2.25em) scale(1,0.05);
        width: calc(100% - 2.25em);
    }
}