static fromCSS(name, css) {
		const themeBuilder = new ThemeBuilder(name);

		// get rules using regex
		const rules = css.match(/:root\s*{([^}]*)}/);
		if (!rules) throw new Error("Invalid CSS string");

		// get variables using regex
		const variables = rules[1].match(/--[\w-]+:\s*[^;]+/g);
		if (!variables) throw new Error("Invalid CSS string");

		// set variables
		variables.forEach((variable) => {
			const [key, value] = variable.split(":");
			themeBuilder(ThemeBuilder.#toPascal(key.trim()), value.trim());
		});

		return themeBuilder;
	}
Creates a theme from a CSS string
@param {string} name
@param {string} css
@returns {ThemeBuilder}