1. CSS3 object-fit/object-position

    Method of specifying how an object (image or video) should fit inside its box. object-fit options include "contain" (fit according to aspect ratio), "fill" (stretches object to fill) and "cover" (overflows box but maintains ratio), where object-position allows the object to be repositioned like background-image does.

  2. css at-rule: `@media`: `aspect-ratio` media feature

  3. css at-rule: `@media`: `device-aspect-ratio` media feature

  4. css property: aspect-ratio

  5. css property: aspect-ratio: auto