CSS code to change letter spacing for uppercase H1 and H2 sitewide

I have the following code added to my website to increase spacing between H1 and H2 header letters from the 0 em set in site styles:

h1, h2{
  letter-spacing: 0.14em !important;
}

This is because H1 and H2 are used in uppercase across my site, so for styling bigger spacing looks best. But, I now want to use H1 and H2 in my blog posts in lowercase and I need the spacing  to be 0 when in lowercase.  Is it possible to alter the coding so the increased letter spacing of 1.4 em only applies when the title is written in uppercase? 

Many thanks

Can you share link to a page where you use uppercase h1/h2? We can check easier

My site isn't published yet so I can't share but I've attached a screenshot . The code has been applied to all the headers in uppercase across the site. This example is 'THE BLOG'. There are about 10 places across the site in total that need the increased space when written as an uppercase heading. The rest of the uses for H1 and H2 are in lowercase and require 0 spacing. Site styles is set at 0 spacing for H1 and H2.

@tizz2930 TuanPhil created a great guide showing you how to share your site if it isn't published yet. Take a look at https://forum.squarespace.com/topic/216243-how-to-setup-password-share-site-url/