Hello, @Kazi Sabit,
In order to solve your issue simply go to the Dashboard >> XStore >> Theme Options >> Theme Custom CSS >> Global and paste the below code at the bottom of the CSS box there.
textarea, textarea.form-control { border-color: red !important; border: solid 1px red !important; }
Then save settings and check back to your site after clearing the browser cache.
The result will appear like this: https://postimg.cc/ctqns7gs
Note: in the above code the word “red” is the color and you can change it with you want.
Regards 8Themes Team.