We are planning to upgrade jquery from 1.8.1 to jquery 3.2.1

The following are currently in use

jquery-1.8.3.js, jquery-ui-1.9.0, jQWidgets v3.1.0

We upgraded as follows,

jquery 3.2.1.js,  jquery-ui-1.12.1, jQWidgets v5.1

After upgrade the entire look and feel of application is changed especially modal dialog stacking is completely changed. I read in a blog that z-index values are reduced from 1000s to 100s in jquery-ui-1.12.1.css.

Is there a way to updrage jquery without changing the look and feel of the existing application. Any suggestions is welcome. Thanks in advance.