Steam requires a specific set of graphical assets for every store page and library entry. Getting the sizes wrong is one of the most common reasons a submission gets bounced during review.
Store assets
- Main Capsule — 1232×706
- Header Capsule — 920×430
- Small Capsule — 462×174
- Vertical Capsule — 748×896
- Page Background — 1438×810 (optional; Valve recommends no text or logo)
Library assets
- Library Capsule — 600×900
- Library Header — 920×430
- Library Logo — 1280×720, transparent PNG only
- Library Hero — 3840×1240 (Valve overlays your Library Logo automatically, so skip the logo layer here)
Use a background of at least 3840px wide so the Library Hero doesn't get upscaled. You can generate every size above from one background/subject/logo composite with the Graphical Assets Generator.