Mastodon Headpats

style.css

.star-icon i {
    display: none;
}
.favorite-button:before, .fa-star:before {
    opacity: 0;
}
.favorite-button, .star-icon, .fa-star, .fa.icon-star {
    background-image: url(https://cdn.niu.moe/custom_emojis/images/000/002/254/static/d9049b5f15505ddb.png);
    background-size: 20px;
    background-repeat: no-repeat;
    background-position: center;
    filter: brightness(1.1) contrast(75%) grayscale(100%) opacity(40%);
}

.detailed-status__link .fa-star {
    background-size: 13px;
}

.fa.icon-star {
    background-size: 16px;
}

.favorite-button.icon-star, .detailed-status__action-bar button.active .fa-star, .star-icon.active, .fa.icon-star.lit {
    filter: brightness(1.1) contrast(75%) opacity(70%);
}

i.star-icon {
    width: 16px;
    height: 16px;
    background-size: 16px;
    filter: brightness(1.1) contrast(75%) opacity(70%);
}

i.star-icon:before {
    content: " ";
}

.notification-favourite > .notification__message > span,
.notification-details span .fa.icon-star + small {
    font-size: 0;
}

.notification-favourite > .notification__message > span bdi {
    font-size: 15px;
}

.notification-favourite > .notification__message > span:after,
.notification-details span .fa.icon-star + small:after {
    font-size: 15px;
    content: " patted your status";
}

.notification-details span .fa.icon-star + small:after {
    font-size: 12px;
}

Still has a star when you highlight a toot but otherwise it works wonderfully!

@cking

Change the start by :

.star-icon i {
    display: none;
}
.fa-star:before {
    opacity: 0;
}
.star-icon, .fa-star {
    background-image: url(https://cdn.niu.moe/custom_emojis/images/000/002/254/static/d9049b5f15505ddb.png);
    background-size: 20px;
    background-repeat: no-repeat;
    background-position: center;
    filter: brightness(1.1) contrast(75%) grayscale(100%) opacity(40%);
}

.star-icon.active, .icon-button.active .fa-star {
    filter: brightness(1.1) contrast(75%) opacity(70%);
}
/* [...] */

It's a nasty hack to fix highlighted toots !

New Version looks like

and we have plemora support