trilium/src/public/javascripts/services/css_loader.js

async function requireCss(url) {
    const cssLinks = Array
        .from(document.querySelectorAll('link'))
        .map(el => el.href);

    if (!cssLinks.some(l => l.endsWith(url))) {
        $('head').append($('<link rel="stylesheet" type="text/css" />').attr('href', url));
    }
}

export default {
    requireCss
}