See screenshot:

Arrow buttons and page buttons should be aligned
Use a PagingPanel with "@devexpress/dx-react-grid-material-ui": "1.7.2", (and all other devexpress packages at 1.7.2 as well) and "@material-ui/core": "3.1.0" The problem does not exist in 3.0.1.
Note - This could very well be my fault - I noticed everything looks fine on your demo page, but I see the package.json uses @material-ui/core": "^3.0.1", which will install 3.1.0. When I use MUI 3.0.1, everything looks great as it always have, but if I change to 3.1.0, I see the issue.
Also, if I remove the height style from .Pagination-arrowButton, the issue disappears. This could obviously be a material issue - please let me know if it seems that way and I can try to open an issue there.
I have the same issue. This could possibly be related to https://github.com/mui-org/material-ui/pull/12865 ?
I believe the issue lies in this changeset in IconButton: https://github.com/mui-org/material-ui/pull/12865/files#diff-fde406414bd717fcea45f653b5632078
They switched from resizing the actual component itself to adjusting its padding whenever changing the size of IconButton.
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Most helpful comment
I believe the issue lies in this changeset in IconButton: https://github.com/mui-org/material-ui/pull/12865/files#diff-fde406414bd717fcea45f653b5632078
They switched from resizing the actual component itself to adjusting its padding whenever changing the size of IconButton.