I am creating a new template and I see that the additional css of the twentyseventeen template is rendered without updating the page instead the additional css of my theme are seen changes after updating the browser window
Additional CSS in the customiser is core WordPress functionality and shouldn't behave differently between themes. You can see in
<style id="wp-custom-css"></style> element to the content of the Custom CSS text field. The
<style> element itself is added by the
wp_custom_css_cb() function hooked into
wp_head at priority
101. So as long as you have the
wp_head() function in your theme, it should behave exactly the same way.