They occur in the stroma - the fluid inside the stroma.
The dark reaction of photosynthesis is also referred to as the light-independent reaction and takes on the name of the Calvin cycle. This is when carbon dioxide and other compounds form glucose, and it does not need light to proceed.
This reaction happens inside the thylakoid. This is the structure of a chloroplast:
It has an outer membrane and an inner membrane, as well as these stacks of thylakoids, called the grana. The light-dependent , so the light reactions take place in the membrane of the thylakoid.
The chloroplast is filled with a liquid called the stroma. It contains the metabolites, molecules and enzymes needed for the light-independent reaction, the dark reaction, or the Calvin cycle.
Hope this helps!