How do I add css?

Thats crazy, you guys call yourselves developers but you cant even edit basic CSS, I need to do mostly animation stuff and polish and fixes, javascript is limited in some cases and some users disable javascript code.

I have a H1 header that I need animated with a gradient, I used this code that worked great, previously I had this working on wix by using the Google Shortcode paste box and it seamed to read that just fine.

background: linear-gradient(134deg, #2ca8bd, #85c776, #6fbfa2, #5dc8dc, #66ea76);
background-size: 1000% 1000%;

-webkit-background-clip: text; 
-webkit-text-fill-color: transparent; 
-webkit-animation: AnimationName 35s ease infinite; 

}

@-webkit-keyframes AnimationName {
0%{background-position:0% 45%}
50%{background-position:100% 56%}
100%{background-position:0% 45%}
}

Basically the header text slowly changes its colors via gradient animation.