[Edit] Fix typo in CSS Overflow entry

[joegorithm]

Description

• Edited the CSS Overflow concept file
• Added a missing colon (:) on line 19 of /content/css/concepts/overflow/overflow.md

It was previously this:

- `hidden` When set to this value, any content that overflows will be hidden from view.

And I changed it to this to match other list items:

- `hidden`: When set to this value, any content that overflows will be hidden from view.

Type of Change

• Editing an existing entry (fixing a typo, bug, issues, etc)

Checklist

• All writings are my own.
• My entry follows the Codecademy Docs style guide.
• My changes generate no new warnings.
• I have performed a self-review of my own writing and code.
• I have checked my entry and corrected any misspellings.
• I have made corresponding changes to the documentation if needed.
• I have confirmed my changes are not being pushed from my forked main branch.
• I have confirmed that I'm pushing from a new branch named after the changes I'm making.
• I have linked any issues that are relevant to this PR in the Issues Solved section.

[CLAassistant]

All committers have signed the CLA.

[mamtawardhani]

Thank you for contributing to Codecademy Docs @joegorithm 😄

The entry looks good for a second round of review! 🚀

[Radhika-okhade]

Thank you for contributing to Codecademy Docs @joegorithm 😄

The entry looks good to be merged. 🚀