create .themerc.js file in your workspace(the project root directory).
module.exports = {
// For now, it only supports `less`, other languages will soon support.
type: 'less',
// you could config a local filePath or use module name like `require`
theme: './your_less_parameters_filePath.less'
};
restart your VSCode, enjoy your style coding with @ triggerChar in your front-end project.