bmi-calculator with SaSS, bootstrap, vanilla JS

I realize that my desktop and tablet designs do not match the provided design for this challenge. In all honesty, I've just spent too much time on this challenge already. Seeing as how this is my first project using SaSS and my second project using bootstrap, I have to say I'm pretty proud. Also the actual js functionality of the calculator took me forever to figure out so I am proud of that too. I've run out of steam on this project and decided to turn it in the way it is so i can move on. I am finding it increasingly tedious to manipulate CSS for responsive design. I feel like i could sit and stare and experiment and fail for hours and hours and this sometimes doesn't seems like a good use of my time. Any suggestions? Does the CSS get easier with experience?