Merhaba, bu kod SCSS kodudur. Css çevirmeden .css uzantısıyla kullanamazsınız.
Aşağıya converted halini yazıyorum. Linkten convert işlemlerini gerçekleştirebilirsiniz.

body {
     font: 400 1em/1.5 "Neuton";
     background: #090d00;
     color: rgba(255, 255, 255, .25);
     text-align: center;
     margin: 0;
}
 p {
     text-transform: uppercase;
     letter-spacing: 0.5em;
     display: inline-block;
     border: 4px double rgba(255, 255, 255, .25);
     border-width: 4px 0;
     padding: 1.5em 0em;
     position: absolute;
     top: 18%;
     left: 50%;
     width: 40em;
     margin: 0 0 0 -20em;
}
 p span {
     font: 700 4em "Oswald", sans-serif;
     letter-spacing: 0;
     padding: 0.25em 0 0.325em;
     display: block;
     margin: 0 auto;
     text-shadow: 0 0 80px rgba(255, 255, 255, .5);
    /* Clip Background Image */
     background: url("https://i.ibb.co/RDTnNrT/animated-text-fill.png") repeat-y;
     -webkit-background-clip: text;
     background-clip: text;
    /* Animate Background Image */
     -webkit-text-fill-color: transparent;
     -webkit-animation: aitf 80s linear infinite;
    /* Activate hardware acceleration for smoother animations */
     -webkit-transform: translate3d(0, 0, 0);
     -webkit-backface-visibility: hidden;
}
/* Animate Background Image */
 @-webkit-keyframes aitf {
     0% {
         background-position: 0% 50%;
    }
     100% {
         background-position: 100% 50%;
    }
}