First, with hack, I tried to duplicate the smiley's second eye using filter: drop-shadow. I used it, because you can't actually use the box-shadow to duplicate the eye.
I used Bootstrap to add a background color, and align the SVG element to center.
Using Sass (Not SCSS) also helped me to save lines. Well, because it doesn't require me to use brackets.
Also the Pug HTML preprocessor, because it doesn't require me to put an end tag in every element.