It is Sunnah to adorn oneself for Eid by wearing one’s best clothes; that does not come under the heading of imitating the non-Muslims

The Muslim should dress for Eid in his
best clothes, and go out to see his friends and visit his relatives looking
and smelling good. This is something that is customary and well-known among
people at all times, and this is their tradition; it is part of expressing
joy and happiness on that day. 

This is also indicated by the Sunnah. 

Al-Bukhaari (948) and Muslim (2068)
narrated that ‘Abdullah ibn ‘Umar (may Allah be pleased with him) said:
‘Umar found a suit of istabraq (a type of silk) being offered for sale in
the market, so he took it and brought it to the Messenger of Allah
(blessings and peace of Allah be upon him) and said: O Messenger of Allah,
buy this and adorn yourself with it for ‘Eid and for the delegations. The
Messenger of Allah (blessings and peace of Allah be upon him) said: “This is
only a garment for the one who has no share in the Hereafter.” The Prophet
(blessings and peace of Allah be upon him did not object to adorning oneself
for Eid; rather he told him that wearing this suit was haraam, because it
was made of silk. 

As-Sindi said in his commentary on an-Nasaa’i
(3/181): 

From this it is known that adorning
oneself on the day of Eid was a tradition that was approved of among them,
and the Prophet (blessings and peace of Allah be upon him) did not object to
it, thus it is known that this tradition is valid and continued. End quote. 

Shaykh Ibn Jibreen (may Allah have mercy
on him) said: 

There are many Sunnahs and mustahabb
actions in Eid prayer, one of which is adorn oneself for it and wear one’s
best clothes. ‘Umar suggested to the Prophet (blessings and peace of Allah
be upon him) that he should buy the suit being offered for sale by ‘Utaarid
and adorn himself with it for Eid and for the delegations, but he rejected
it because it was made of silk, and he had a suit that he would wear on Eid
and on Fridays. End quote. 

Fataawa ash-Shaykh Ibn Jibreen
(59/44) 

Al-Haafiz Ibn Jareer (may Allah have mercy
on him) said: Ibn Abi’d-Dunya and al-Bayhaqi narrated with a saheeh isnaad
going back to Ibn ‘Umar that he used to wear his best clothes on the two
Eids. End quote. 

Shaykh Ibn ‘Uthaymeen (may Allah have
mercy on him) said: 

It is Sunnah for men on Eid to adorn
themselves and wear their best clothes. End quote.

Majmoo‘ Fataawa wa Rasaa’il Ibn
‘Uthaymeen (13/2461) 

So there is nothing wrong with a Muslim
buying new clothes for the day of Eid, and that does not come under the
heading of imitating the non-Muslims, even if they do that on their
festivals and celebrations. With regard to everything that shar‘i evidence
indicates is prescribed and recommended, doing it cannot come under the
heading of imitation of the disbelievers that is prohibited. 

With regard to good attitudes, for
example, treating people kindly, being cheerful when meeting people,
cleanliness, wearing perfume and other things that are prescribed, and there
is shar‘i evidence to indicate that they are prescribed and recommended, the
fact that some non-Muslims also do some of these things does not matter. 

The imitation of disbelievers that is
prohibited is doing things that are unique to them. As for things that are
common to all people, and are not unique to the disbelievers, there is
nothing wrong with the Muslims doing them. 

Shaykh Ibn ‘Uthaymeen (may Allah have
mercy on him) was asked about the guidelines on imitating or resembling the
disbelievers. 

He replied: 

The guidelines on imitation refer to when
the imitator does something that is unique to the one who is imitated. So
imitating the disbelievers means that the Muslim does something that is
unique to them. As for things that have become widespread among the Muslims,
and are no longer unique to the disbelievers, that does not come under the
heading of imitating or resembling others, so it is not haraam on the
grounds that it is an imitation of the non-Muslims, unless it is haraam for
some other reason. What we have said here is what is indicated by this word,
and something similar was stated by the author of al-Fath when he
said: Some of the early generations regarded it as makrooh to wear the
burnoose, because it was the clothing of (Christian) monks. Maalik was asked
about it and said: There is nothing wrong with it. It was said: But it is
the clothing of the Christians. He said: It is worn here. End quote. 

Majmoo‘ Fataawa wa Rasaa’il Ibn
‘Uthaymeen (3/47-48) 

See also the answers to questions no.
36442 and
108996

And Allah knows best.