Castrol/Girling are Europes largest manufacturer of Oils and fluids, the one you have chosen is perfect for what you want, DOT 4. Be very careful to keep the container tightly sealed at all times, Brake fluid is hygroscopic (absorbs water) and containers must be kept air tight. The electronics you see in the cap are a part of the fluid level indicators and will not come to any harm.
If your system is losing fluid it might be a good idea to have it checked by your Volvo shop, you should certainly not have to add more than a teaspoon or so as part of routine maintenance.
John Scales (1966 850R)