Adding margin above standalone video levels

[daynew]

Adding back a small space between the Code.org header and videos on standalone video levels. This was accidentally removed in a previous PR which made banner and header changes.

Testing story

• localhost

Screenshots

Before

Note the lack of space between the teal code.org header and the youtube video.

After

Reviewer Checklist:

• Tests provide adequate coverage
• Code is well-commented
• New features are translatable or updates will not break translations
• Relevant documentation has been added or updated
• User impact is well-understood and desirable
• Pull Request is labeled appropriately
• Follow-up work items (including potential tech debt) are tracked and linked