efecto-blur.css

body {
    margin: 0;
    padding: 0;
    display: flex;
    justify-content: center;
    align-items: center;
    background: linear-gradient(darkblue, aqua);
    height: 100vh;
}

ul {
    margin: 0;
    padding: 0;
    display: flex;
}

ul li {
    list-style: none;
    margin: 0 15px;
    transition: .4s;
}

ul li a {
    display: block;
    text-decoration: none;
    position: relative;
    font-family: Verdana, Geneva, Tahoma, sans-serif;
    color: azure;
    font-size: 18px;
    padding: 7px;
    transition: .4s;
}

ul:hover li a {
    transform: scale(1.4);
    opacity: .2;
    filter: blur(4px);
}

ul li a:hover {
    transform: scale(1.8);
    opacity: 1;
    filter: blur(0);
}

ul li a:before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    background: black;
    width: 100%;
    height: 100%;
    transition: transform .4s;
    transform-origin: right;
    transform: scaleX(0);
    z-index: -1;
}

ul li a:hover:before {
    transition: transform .4s;
    transform-origin: left;
    transform: scaleX(1);
}