Four icons, one file

Both columns send their four icons as a single request. Make the icons bigger with the slider (it needs JavaScript), then switch your system to dark mode, and compare.

CSS sprite: one PNG

icons-sprite.png: 192 by 48 pixels. Drawn in a fixed navy, so it fades on a dark background, and it blurs once it is shown larger than 48 device pixels.

SVG sprite: one file of symbols

icons.svg: four <symbol> elements. Stroked in currentColor, so it follows the text color and dark mode, and it stays sharp at every size.