With bootstrap, it's always a good idea to see what is already out there when wanting to do something like this. Bootstrap has a lot of features that can easily be used.
https://higuma.github.io/bootstrap-4-css-customization/en/gradient+shadow.html is an example of what can be done with existing gradients in bootstrap 4 and the bg-gradient-xxxxxx class. It gets deep but is a thorough cover of the topic.
You could create a rule in the site-specific something like```
.myGradient {color: #721c24;
background: #f8d7da linear-gradient(180deg,#f9dde0,#f8d7da) repeat-x;
border-color: #f5c6cb;
}
Then add it to the items that you want to have that gradient.
It might be easier to use several different div's and classes instead of the .myGradient.```
.leftBoxHeading, .centerBoxHeading, #navMain { color: #721c24;
background: #f8d7da linear-gradient(180deg,#f9dde0,#f8d7da) repeat-x;
border-color: #f5c6cb;
}
This saves having to tooch a bunch of core files.
Still there is the option of having several gradients and just adding the class/div to a particular item.