The padding-inline-start property defines the padding space on the “start” side of an element’s inline axis - that is, it increases the distance between the element’s content and its border on the inline-start edge. Because it is a logical property, the exact physical side it affects depends on the element’s writing direction and writing mode: in a left-to-right horizontal flow it corresponds to the left edge, while in a right-to-left flow it corresponds to the right edge, and in vertical writing modes it maps to the appropriate inline-start edge for that mode. The property itself does not inherit; it affects the element’s box and therefore influences layout, hit testing, and how background and border are drawn around content.

Logical properties like padding-inline-start are designed to work together: it is typically used as a pair with padding-inline-end to express inline-axis padding in a direction-agnostic way. When needed, you can relate them back to the traditional physical properties - for example, the logical start side corresponds to one of the physical paddings such as padding-left or padding-right, depending on the content flow. Choosing logical properties makes styles more robust across localizations because they automatically adapt when the document’s direction or writing mode changes.

In practice, padding-inline-start interacts with other CSS declarations in predictable ways: it can be overridden by later rules or by a shorthand such as padding, and changes to layout direction via properties like direction or writing-mode will alter which physical edge is affected without changing this logical declaration. Because of that, it is a recommended tool when you want spacing that remains correct across languages and scripts - for example, when aligning icons or leading content consistently at the start of lines regardless of whether text flows left-to-right or right-to-left.