My team complains that interface is too bright.
I did check the 'Look and Feel' section in the System Admin menu, but it allows me only to change the Side (or Top) menu colors.
Sorry to report that there is not a way to customize all colors within Jira natively within the browser without either hacking at the source code or perhaps a 3rd party plugin might do this.
I found a number of feature requests for this behavior those such as https://jira.atlassian.com/browse/JRASERVER-63150
In my search I cam across a user created style in https://userstyles.org/styles/116546/jira-dark-theme
I am not familiar with this stylish site, but this appears to be a theme that you can use with an extension to your chrome or firefox browsers as a means to change the way the page is rendered to the end user. This solution isn't ideal because each of your users would need to install this separately, but it might help provide some kind of work-around until such time as Atlassian provides another means to customize this aspect within the product itself.
Alternative to that I also came across this Jira Server plugin: Dark Theme for Jira. It appears this plugin can do what you want in Jira, however there is a cost for the use of this plugin.
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