In brief
align-items sets shared item alignment; in flex it acts on the cross axis. In an icon-and-text row, center can align their centres.
Useful to know
align-items sets shared item alignment; in flex it acts on the cross axis. In an icon-and-text row, center can align their centres. [1]
This differs from aligning text baselines. For a typographic row, compare baseline too, and identify the cross axis again when the flex direction changes to a column.
Sources
For further detail and to check the information: