style.css

@keyframes color {
    0% {color: rgba(153, 0, 0, .8);}
    10% {color: rgba(153, 204, 0, .8);}
    20% {color: rgba(153, 207, 255, .8);}
    30% {color: rgba(0, 100, 255, .8);}
    40% {color: rgba(0, 157, 54, .8);}
    50% {color: rgba(0, 212, 209, .8);}
    60% {color: rgba(0, 255, 0, .8);}
    70% {color: rgba(255, 255, 0, .8);}
    80% {color: rgba(255, 143, 0, .8);}
    90% {color: rgba(96, 232, 172, .8);}
    100% {color: rgba(153, 0, 0, .8);}
}

* {
    margin: 0;
    padding: 0;
}

*::selection {
    color: #00B390;
}

html, body {
    height: 100%;
    width: 100%;
}

body {
    flex-direction: column;
}

.flex {
    display: flex;
    justify-content: center;
    align-items: center;
}

.wrapper-title {
    flex-direction: column;
    margin-bottom: 10%;
    margin-top: -10%;
}

h1 {
    font-size: 4em;
}

h2 {
    font-size: 2em;
}

h1,h2 {
    animation: color 40s linear infinite;
    text-shadow: 0 0 5px #000;
}

a {
    display: block;
    text-decoration: none;
    color: #0000ff;
    font-size: 25px;
    margin: 0 25px;
    transition: 0.4s;
    text-shadow: 0 0 2px black;
}

a:visited {
    color: black;
}

a:hover {
    transform: scale(1.5);
    color: red;
    text-shadow: 0 0 15px red;
}

a:after {
    display: block;
    content: '';
    height: 1px;
    width: 0%;
    background: red;
    transition: 0.4s;
}

a:hover:after {
    width: 100%;
}