Soak a soft cloth in lukewarm water mixed with a small concentration of pH-neutral detergent (e.g. dishwashing liquid). Do not use Handy Andy. Wipe dry afterwards.
Although sealed, concrete is still porous and might get stained by oils or liquids containing strong pigments.
The colour of concrete can change over time depending on environmental conditions.
The concrete tabletop will need to be re-sealed from time to time.