I was wondering about wearing make-up, like eyeliner or lip-gloss outside of the house. I know that we should not display beauty, but I have also heard that it is important to look nice in Islam, for Allah loves beauty, and that Muslims should always be clean, wear nice clothes, etc. I was wondering about wearing eyeliner, since my eyes are very small and dull, and just wearing a thin line to enhance my eyes, makes them look better, but natural. Is that permissible?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

You are right that Allah loves beauty and a Muslim should wear good and clean clothes so that he has a decent appearance.

Allah Says (what means): {And your clothing purify.} [Quran 74:4]

Besides, the Prophet, Prophet said: “Allah is Beautiful and He loves beauty.” [Muslim]

Thus, it is legitimate for men and women to beautify themselves with what Allah, The Exalted, has made lawful for them.
Here, the use of make-up is included in the above-general ruling; i.e., a woman can wear items such as lip gloss, or eye liner, but she should not appear in the same state in front of non-Mahram men or non-Muslim women. In addition, she has to wear her complete Hijaab when she leaves her home.

Allah Says (what means): {O Prophet, tell your wives and your daughters and the women of the believers to bring down over themselves [part] of their outer garments. That is more suitable that they will be known and not be abused. And ever is Allah Forgiving and Merciful.} [Quran 33: 59]

For more benefit on women wearing make-up when going outside, please refer to Fataawa 129259, 122891, and 90876.

Allah knows best.