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Any paid theme is going to be better than a free one. Yes it’s an investment. But one that is definitely worth it. You could literally spend hundreds of hours trying to get a free theme like dawn or horizon the way you want. Or get something that already has the features and settings built in. Its been done, and there are successful websites built on dawn, but it’s not worth it imo. Plus, in the Shopify Store you can try before you buy. Check out some premium themes. You may like some, and not like others. As for me, I prefer Themeforest themes. They have way more bells and whistles for a lot cheaper, and the developers are available through chat and give one on one help for up to 6 months I think.
Put announcement-bar before header in theme.liquid.
Give bar a higher z-index (e.g., 9999) and the header a lower one (e.g., 1000), both with position: relative (or sticky/fixed if your design needs it).
If the bar is fixed, add top space (CSS padding or the small JS that measures the bar).