Katy here from Shopify. Thank you for posting.
It seems that your picture has not uploaded here, so I am unable to see your example. However not to worry, I would love to help.
You can adjust the text size of your product description, by adding some code to your theme's CSS.
You can access this via your Admin > Online store > Themes > Edit Code > Assets > theme.scss.liquid
At the very bottom place the following code:
You can then feel free to adjust the sizing accordingly if you like.
I hope this helps you out- do feel free to let me know!
Hello Katy and thanks for your speedy answer.
I added the code at the very bottom place of theme.scss.liquid but did not affect anything.
I took another screenshot for the store. You can see the text size is little different in size. How can I make it all in same size?
Apologies for the delay in getting back to you, and that this option did not work.
I have taken a closer look, and this may be due to the theme you are using.
We can also try to edit this via your product-template.liquid file.
If you could go to your Admin > Online store> Themes > Edit code as before, and from here click into ' sections' and product-template.liquid.
Here, if you search from 'description' and insert the following piece of code like so:
; <p style="font-size:14px">>
This should allow you to adjust the text accordingly. Do keep in mind that this will change if you use a different product template in future.
I hope this helps. Do feel free to let me know.