In Power BI, the three major styles of conditional formatting available are as follows:

Gradient-Based

With this type of style, a gradient color scale is assigned to the cells, implying that the color will change depending on the values in the data. The color will smoothly graduate from one end of the spectrum to the other. This helps in showing at a glance any pattern in the distribution of data.

Rule-Based

Highlighting is performed by this style. That is, certain rules are followed to apply some formatting based on the values in the cells. For instance, it could be used to highlight cells that meet specific criteria for above or below a threshold or within a defined range.

Field Value-Based

Applying through this style, formatting is driven by a measure that outputs color in text or hexadecimal format. Then, conditional formatting is applied with the results of these measures to achieve more dynamic, custom formatting.