/* Apply class="todo" to any element. */
.todo {
    color: #b00020;
    background: #fff700;
    padding: 0.1em 0.35em;
    border-radius: 0.2em;
    box-shadow: 0 0 0.5em rgba(255, 230, 0, 0.8);
    animation: todo-glow .5s ease-in-out infinite alternate;
}

.todo::after {
    content: " TODO";
    color: #d00000;
    font-weight: 900;
    letter-spacing: 0.08em;
}

@keyframes todo-glow {
    from {
        box-shadow: 0 0 0.25em rgba(255, 230, 0, 0.65);
    }
    to {
        box-shadow:
            0 0 9em rgba(255, 230, 0, 1),
            0 0 18em rgba(220, 0, 0, 0.55);
    }
}