如何使用外部CSS将作为新行？

I am new to stack overflow and I'm trying to make a mobile webpage from the existing desktop version webpage someone else created. Basically, I have to use same webpage for both mobile and desktop. For this specific page with table, I am trying to change the pattern of table for mobile using external style sheet.I had attached the html skeleton and css with this post. Initially, there is only one row with two s. I want to bring ".td2" to new in next line. I tried a basic table in which I was able to bring down all converted to tr worked but in this case, second containing a table is making me hard. I tried all the way I could. I will be helpful if someone help me.I am new to stack overflow and I'm trying to ma