Fow now, many people rely on the block styles provided by the themes' CSS properties. However, this way causes styles to be lost when switching themes. Luckly, a new plugin has recnetly been released in the marketplace, it allow you add CSS properties in block menu.

However, it's important to note, that by adding styles using this method, your styles may only be compatible with light color themes.

And, this plugin can't set CSS properties for many blocks in same time for now.