Change font style in entire JIRA Application

[Approver1]

Hi, Please find the Below screenshots for reference:

In below image from Old Server, 

In below screenshot from New Server. 

 

In both server font and color size are different. how to change the JIRA default font style to required font style...Please suggest us

[Kirstin Seidel-Gebert]

Hi Chandramouli,

you can customize Jira with your own CSS via the announcement banner as described in this community post:
Customize Jira with my own css 

Cheers,
Kirstin

[Approver1]

Hi @Kirstin Seidel-Gebert 

Old server announcement banner:

Nothing is there in Old server announcement banner...But font has different how?

[Kirstin Seidel-Gebert]

I do not know of way to set the font in Jira via the UI of the application... Sorry.

I googled a bit, and found this, though: changing the default font in jira Atlassian JIRA 
But I guess you do not want to change the application files. This is really the hard way (as described in the linked post).