.runway { height:calc(var(--n) * 100vh); }
.part { position:fixed; inset:0; z-index:6; pointer-events:none; opacity:0; }
.part .head { width:330px; }
.part .glass { z-index:7; }
body, nav .btn, .part .btn { transition:color .6s var(--ease), background-color .6s var(--ease); }
html[data-dark] body { color:var(--light); }
html[data-dark] nav .btn { background:var(--bone); color:var(--ink); }
html[data-dark] .part .btn { background:var(--bone); color:var(--ink); }
html[data-dark] .grain { mix-blend-mode:screen; opacity:.05; }