.btn {
    position: relative;
    display: inline-block;
    padding: 6px 12px;
    color: #333;
    font-size: 16px;
    font-family: 'Open Sans', sans-serif;
    font-weight: 400;
    text-align: center;
    text-decoration: none;
    transition: .3s;
    border-radius: 8px;
    background-color: rgb(0, 0, 0, 0);
    border: 1px solid #333;
}

button.btn{
    border: 1px solid #333;
}

.btn::before {
    position: absolute;
    top: 0;
    right: 0;
    bottom: 0;
    left: 0;
    z-index: -1;
    content: '';
    background: #333;
    border-radius: 5px;
    transition: transform .3s;
}
.btn:hover {
    color: #fff;
    background-color: rgb(51, 51, 51, 0);
}
button.btn:hover {
    border: 1px solid rgb(51, 51, 51);
}

.btn::before,
.btn::after {
    position: absolute;
    top: 0;
    right: 0;
    bottom: 0;
    left: 0;
    z-index: -1;
    content: '';
    border-radius: 5px;
    transform: scale(0, 1);
}

.btn::before {
    background-color: #666;
    transform-origin: right top;
    transition: none;
}

.btn::after {
    background-color: #333;
    opacity: 0;
    transform-origin: left top;
    transition: transform 0s .3s, opacity .3s;
}

.btn:hover::before {
    transform-origin: left top;
    transform: scale(1, 1);
    transition: transform .3s;
}

.btn:hover::after {
    opacity: 1;
    transform-origin: right top;
    transform: scale(1, 1);
    transition: transform .3s .3s, opacity .3s;
}