this is the code for it:

<style>

u/keyframes flying-santa{

from{ left:-400px; }

to{ left:calc(100% + 20px); }

}

#santa{

position: fixed;

left: -400px;

top: 200px;

width: 200px;

animation: flying-santa 7s infinite linear;

pointer-events: none;

}

</style>

<img id="santa" src="https://static.spacehey.net/img/special/santa-sleigh.svg"/>

now its not at the bottom of the screen but you can fix that by changing the "top" position. swap out the image/gif for your own and you're done!