While many things in the frontend can be configured using the frontend itself, some customisations are currently only possible by editing a definitions file.
This file is
defines.inc.php located in /include of the Zabbix HTML document directory.
Parameters in this file that could be of interest to users:
Minimum graph period, in seconds. One hour by default.
Default location of Y axis in simple graphs and default value for drop down box when adding items to custom graphs. Possible values: 0 - left, 1 - right.
Used in screens and defines the timeout seconds for a screen element update. When the defined number of seconds after launching an update pass and the screen element has still not been updated, the screen element will be darkened.
Used in screens and defines the number of seconds after which query skipping will be switched off. Otherwise, if a screen element is in update status all queries on update are skipped until a response is received. With this parameter in use, another update query might be sent after N seconds without having to wait for the response to the first one.
Defines retrieval limit of the total items queued. Since Zabbix 3.2.4 may be set higher than default value.