We’re limited in helping with styling customizations, per our Scope of Support / Terms. But a few tips to help you carry this further include:
Start by modifying what you can at Appearance » Customize » The Events Calendar.
We generally don’t recommend that you change the theme or plugin’s CSS files directly, as they will be overwritten. To avoid this, follow the steps outlined in Themer’s Guide
Use overriding CSS files, or add CSS to your site using Appearance » Customize » Additional CSS.
Use !important before a semicolon to override every css rule. It’s a brute force method, but works for quick fixes.