🐛 BUG: w3c validation

[jurjendevries]

Describe the bug
Multiple pages have w3c validation errors. For example see https://validator.w3.org/nu/?doc=https%3A%2F%2Fdilmahtea.me%2Fen%2F for the homepage.

Steps to Reproduce
Steps to reproduce the behavior:

1. Go to https://validator.w3.org/nu/?doc=https%3A%2F%2Fdilmahtea.me%2Fen%2F
2. See errors and warnings

Expected behavior
Fully w3c compliance, so no errors and warnings.

Screenshots
If applicable, add screenshots to help explain your problem.

Desktop (please complete the following information):

N/a

Smartphone (please complete the following information):

N/a

Additional context
Some errors and warnings are on multiple pages. So solving them once mostly helps solve them on all pages. Please check all type of pages with w3c validation