Drag and drop and hotspot question background (width):
750 px.
Single choice image question:
Thumbnail - 260x260 px.
Image layouts (width):
Image on the left/ right/ two images: 420 px; One image: 880 px.
Section icon:
220х255 px.
Course logo:
360x200 px, depending on the logo shape.
Background:
Cover background image - 768x1024 px (3:4 ratio).