If this is in concert with something like a tooltip bubble, or similar, using it as an arrow, I think you could make it *somewhat* responsive, by replacing px values with em or rem. If your body has the typical font-size: 62.5%; so that 1em is *usually* 10px, then the math is easy when using rem, and not terribly difficult for em.
The trick would be to set media query breakpoints that appropriately reset font-size at lower resolutions. Ideally, you could use em as a base unit, reduce font-size only on the immediate parent element of the triangle (thus effecting the triangle, but nothing else on the page), and it would shrink the triangle.
Edit: Yeah, I **cannot** seem to get this to work in practice. Nevermind, I suppose.