Saw the errors and looks like the plugin is trying to make the widget settings work by inserting style element inside the body making the validator to complain.
We do not have much control over the code of this plugin and I wanted to leave the theme open to plugin updates instead of making custom changes and bundling with the theme itself (APIs can change and plugin authors are best ones to handle the same). I handle only some part of plugin styling to make it work well with the theme.
I would suggest you give a shot at below one and see if it meets your need ( I haven’t tried it myself yet). Thanks –