Dress codes vary with position within the company, industrial sector and region in France.
The higher the position within a larger organisation, the more formal will be the dress code with formal suit and tie being worn.The further south one travels, the more informal business dress becomes, with open shirt and slacks being the norm.
One thing that is common to all areas and all positions however is the need to appear well-presented. Casual does not mean scruffy. Appearances are important at all times in France.