It's not about making it "look good". Completely subjective. The app needs the capbility to switch out the CSS.
For instance, we resell/implement a popular cloud app - just our company - we do dozens of large implementations.
Out of box, this app has a super modern look! It is not the SAP etc.. of days gone by. Even with this, some love it, some hate it. Waste of time trying to guess what people think looks good.
Put their logo on, probably 8 out of 10 ask for this. No brainer.
Need custom CSS, 1 out of 20 ask for this. App should be able to.
If they want to get crazy, the capability for complete custom pages. Maybe 1 out of 50 customers ask for this and after you quote them the price they'll not want it.
Out of box, this app has a super modern look! It is not the SAP etc.. of days gone by. Even with this, some love it, some hate it. Waste of time trying to guess what people think looks good.
Put their logo on, probably 8 out of 10 ask for this. No brainer.
Need custom CSS, 1 out of 20 ask for this. App should be able to.
If they want to get crazy, the capability for complete custom pages. Maybe 1 out of 50 customers ask for this and after you quote them the price they'll not want it.