Hi there,
The first intention of the suggestion of a code with the ID was to restrict the code to only the form in question and not other possible contact form 7 forms on the website.
Please kindly consider that this a customization request and outside of our support scope, we can not give you code for each part of changes you want to do and you either need to hire a developer for that or learn how to utilize CSS and proper selectors.
I suggest that you remove the ID from your code altogether. But you need to add an HTML class instead which will represent the styling you want. You can wrap the whole form in the contact form 7 options with a div
tag with proper class. For example, the code below wraps the whole form with a div tag with the class of light-form
:

Now in the CSS code, you can use the code below instead of the ID:
.light-form textarea {/* YOUR CSS CODE HERE */}
Now you can apply the styles you want for the light-form class. If you want to have another styling for your forms you can wrap it to a div tag with other class name and add the CSS code to that class.
This is indeed not part of our theme or normal usage of the contact form 7 with default styling of the theme. This is a customization request and the implementation of the code is on your shoulders. The last thing that we can be of a help is to give you resources that you can read for further customization. I did a Google Search regarding this that might get you started with proper coding.
Thank you for your understanding.