Distinguishable

Two elements are distinguishable if they are both visible, and there is a difference in the computed value of one or more of the following CSS properties:

background-color, background-image;
border-width, border-color (or any of their longhand properties);
box-shadow];
font-family, font-weight;
outline-width, outline-style, outline-color;
text-decoration-color, text-decoration-line;
vertical-align;
the highest possible contrast ratio between their foreground colors is 3:1 or more;

Additionally, a hovered element is distinguishable from another element if there is a difference in the computed value of their cursor property.

Any difference in background-image is considered sufficient, even if these ultimately resolve to the same actual image. This definition does not try to compare the images.