.title-1 {
    position: relative;
}

.title-1:before {
    content: '#';
    opacity: 0.7;
    position: absolute;
    left: -15px;
}

.title-2 {
    position: relative;
}

.title-2:before {
    content: '#';
    opacity: 0;
    position: absolute;
    left: -15px;
    transition: opacity .2s;
}

.title-2:hover:before {
    opacity: 0.7;
}