Tip calculator app (SASS and JS)

Hello, I have completed this exercise!

The logo is slightly off centre when I give it left: 50% relative to the calculator container for some reason. I had to change it to 48% to be as centre as possible. If anyone can point out the reason why, it would be very nice!

On Javascript, I used isValid as a boolean array with 2 values to activate the reset button if both input values are valid, and if the tip is chosen. If there is a better way to do it, please let me know.

Thank you for reading, any feedback is appreciated!