Responsive Section (Quick fix im sure)


This is my first post! I am usually pretty good at figuring things out but since i’ve dove into the deep end following the custom portfolio tutorial I’m having some trouble figuring out how to fix the following.

In mobile portrait when I move to the narrowest option the selected list disappears off the screen. I have tinkered around with size etc but am not sure why it won’t stay on the screen. Also, i am curious to know why it ‘snaps’ the pixels when moving, there is no smooth transition. I am a new designer here so any help is appreciate, no matter how simple it may be!