thedesk/app/js/ui/theme.js

//テーマ適用
function themes(theme) {
	if (!theme) {
		var theme = localStorage.getItem('customtheme-id')
		if (!theme) {
			localStorage.setItem('customtheme-id', 'black')
			theme = 'black'
		}
	}
	postMessage(['themeCSSRequest', theme + '.thedesktheme'], '*')
	var el = document.getElementsByTagName('html')[0]
	el.style.backgroundColor = 'var(--bg)'
	var font = localStorage.getItem('font')
	if(font) {
		el.style.fontFamily = font
	} else {
		el.style.fontFamily = ''
	}
}
themes()