First of all, I don’t recommend you to edit the theme files.
Next, If you want to customize your theme, please use the built-in options from the customizer ( Dashboard->Appearance->Customize)
There you can find many options to customize the look of your theme.
e.g if you want to change the height of the breadcrumb, you can go to Customizing-> Breadcrumb -> General…
And change the height per your needs
Also, If you want to change the page background color, simply go to : Customizing ▸ General ▸ Pages menu and pick your favorite page background color,
If you want to add some custom CSS codes, instead of the modifying theme CSS files, simply insert it into the Customizing->General->Additional CSS
If you find that some options missing and you need some additional help with custom CSS, I can help you with that.
Also, please check our knowledge base at the following address: