How to compile all styles into one css file via VS Code Live Sass Compiler?

Question

Visual Studio Code

Suppose I have an old css file Old_style.css, where all the styles for the site are stored.

I want my new edits that I make through .scss to be immediately compiled into Old_style.css and work on the site ==> I create a file Old_style.scss in the sass folder

But instead of adding new styles in the same file (Old_style.css), sass creates in a completely new file ==> all old styles are lost.

Is there a way to fix this in the settings?