Cannot find code in theme

I wanted to modify the existing theme but didnt find liquid code.

You can only modify custom themes, not the built-in themes.

So, if there’s a built-in theme you would like to modify, you first need to clone it as a custom theme. Click to view it, then click on “Copy to” (next to “Edit”), then “New Theme”. This will display the code for editing, and allow you to give the theme a new name. This will now be a custom theme, and you can come back and edit it at any time.

Read the Guide:

Great thank you to both Tut and GrahamvdR. It was a great guide. I am able to change according to my desire with few html and css code. Once again thanks a lot.