div is not responsive to the browser screen?

I was able to replicate the problems here. I think the issue is around margin applied on the class tof. To fix, you can use css media queries styles below

@media only screen and (max-width: 480px) {
    .tof {margin: 20px;}
    .grid-container { grid-template-columns: repeat(1, 1fr) !important;overflow: hidden;}
}

@media only screen and (max-width:768px) {
    .tof {margin: 20px;}
    .grid-container { grid-template-columns: repeat(2, 1fr);overflow: hidden;}
}