thedesk/app/js/ui/theme.js

//テーマ適用
function themes(theme) {
	if (!theme) {
		var theme = localStorage.getItem("theme");
		if (!theme) {
			var theme = "black";
			localStorage.setItem("theme", "black");
		}
	}
	var el = document.getElementsByTagName("html")[0]

	el.classList.remove('indigotheme');
	el.classList.remove('greentheme');
	el.classList.remove('browntheme');
	el.classList.remove('blacktheme');
	el.classList.remove('bluetheme');
	el.classList.remove('customtheme');
	el.classList.add(theme + "theme");
	var font = localStorage.getItem("font");
	if (font) {
		el.style.fontFamily = font;
	} else {
		el.style.fontFamily = "";
	}
	if (theme == "custom") {
		if (localStorage.getItem("customtheme-id")) {
			postMessage(["themeCSSRequest", localStorage.getItem("customtheme-id")], "*")
		}
	}
	el.style.backgroundColor = "var(--bg)";
}
themes();