One key condition: wear "decent" attire. Working the counter at a bank in sweatpants? Your employer can discipline you or even dismiss you. That said, as long as your outfit doesn't harm the business, you have the freedom to choose.
French labor code allows requirements for dress, hairstyles, or makeup when justified by the role. Picture working at Sephora without makeup or at Dessange with unkempt hair—it's unprofessional. Hotels and event hosting often mandate uniforms. These must be specified in internal regulations, collective agreements, or your employment contract. Refusal risks dismissal for serious misconduct.
For uniforms—logoed items or those sold by the company (like in retail)—your employer provides them. Otherwise, you're responsible, such as grabbing a black skirt from H&M. They can't impose excessively costly attire.