I've had quite a few people ask me for help making Zoho CRM webforms responsive. My standard answer is "don't even try". The forms look bad anyway and are hard to work with. A better option is to use Ninja Forms (a wordpress plugin that makes nice looking forms that integrate with Zoho CRM).
If you do want to persist with using Zoho CRM's webforms, this video explains an approach to making them responsive. I've built a little utility that does some of the work for you. You'll still need design skills to make the forms look nice afterwards but it might save you some time.
Here's the video showing it in action: