Merge pull request 'GPU acceleration for the mobile menu' (#818) from gpu-acceleration into main

Reviewed-on: https://git.joinplu.me/Plume/Plume/pulls/818
Reviewed-by: kiwii <kiwii@noreply@joinplu.me>

assets/themes/default/_header.scss

@@ -205,6 +205,7 @@ body > header {
    		position: absolute;
    		left: 50%;
    		transform: translate(-50%, 0);
+   		transform: translateZ(0);
    		opacity: 0;
    		font-size: 0.9em;
    		white-space: nowrap;