I just installed the template, create a menu for test and bind the template on that. At Modules menu, create one Gantry Particle Slideshow, bind it on "fullwidth" position and call my URL.

Message appers: "Missing content: 'slideshow-joomla' particle cannot be found."

At templates/it_startup/scss/startup.scss i have

// Slideshow Particle

@import "startup/slideshow

At templates/it_startup/startup i dont have any _slideshow.scss file. So, i download the Slideshow Particle and upload the file _slideshow-joomla.scss.

Message appers: "Missing content: 'slideshow-joomla' particle cannot be found."

I realized that at templates/it_startup/scss/startup.scss the @import is not the same name of my message error and file name. So, i change the code at templates/it_startup/scss/startup.scss to

// Slideshow Particle

@import "startup/slideshow-joomla

Message appers: "Missing content: 'slideshow-joomla' particle cannot be found."

Question 1: Why did not the template work if it already contains all the particles?
Question 2: After all my changes, what i missing?

[Joomla 3.7.3] [Gantry 5.4.14]