:root{--bg: #ffffff;--fg: #111111;--accent: #0066cc}:root[data-theme=dark]{--bg: #111111;--fg: #eeeeee;--accent: #66aaff}body{background:var(--bg);color:var(--fg);transition:background .2s,color .2s}#theme-toggle{position:fixed;top:1rem;right:1rem;background:none;border:none;cursor:pointer;font-size:1.4rem;line-height:1}