refactor: tighten up css

created a bunch of utility classes and use those instead

src/lib/Avatar.svelte

@@ -5,9 +5,9 @@
  export let size: string = 'var(--avatar-size)';
 </script>
 
-<div class="avatar" style:--color="{color}" style:--size="{size}" on:click>
+<button class="avatar pa-0 border-0" style:--color="{color}" style:--size="{size}" on:click>
     <img src="{avatar}" alt="{`${username}'s avatar`}">
-</div>
+</button>
 
 <style>
  .avatar, .avatar > img {