If you decide you do not want to use the Block Editor (Gutenberg editor) that is now the default editor for WordPress (version 5), you can disable the stylesheet that our theme has. All themes past the Salal theme now have the block styles separate from the theme to keep the stylesheet smaller and to prevent any style conflicts.
Go to Appearance >> Customize >> Theme Options >> Basic Settings
Look for the “Disable the Block Stylesheet” setting and check the box to disable it.
Click “Save & Publish“.