By default some blocks have background white, you might need to add a background color, to do this simply copy the main class of the block then go to 'Site administration' then 'Appearance' followed by 'Nice learning' then 'Advanced settings' add the class name with the background you want.

Here are some classes you might need to add a background:

• .nice-featured-course-container
• .nice-categories-slider-1
• .nice-categories-slider-2
• .nice-courses-slider-1
• .nice-courses-slider-2
• .nice-courses-slider-3
• .nice-courses-slider-4
• .nice-courses-slider-5
• .nice-blogs-slider-1
• .nice-blogs-slider-2
• .nice-instructors-slider-1
• .nice-testimonials-slider-1
• .nice-testimonials-slider-2