Responsive Order Summary Component using Flexbox (Responsive)

Nothing seemed that difficult in this Project. Though I've some Questions :

• How was the HTML?
• Was it semantic enough?
• How about the class names were they also semantic?
• Should all text type elements p, h1 etc. have class names?
• Is it a good practice to specify something like h3 compared to .container h3 if you know that only one h3 will be on the page? Suggest me some better practices which I should use in upcoming projects to make them more efficient. Any Feedback is appreciated : )