DNA is negatively charged due to the presence of phosphate groups in its nucleotides. This negatively charged DNA wraps around the positively charged histone proteins to form a nucleosome. A typical nucleosome has 200 bp of DNA.
Histones are rich in basic amino acids like lysine and arginine which carry positive charge in their side chains due to which they are positively charged.
Apart from histone proteins, the packing of chromatin at higher levels requires an additional set of proteins that collectively are referred to as non-histone chromosomal proteins (NHCs).