Many fields in the zabbix front end are for data that does not fit into any human language - for example item keys, and trigger expressions.  Most modern browsers have a spell check feature which will underline or otherwise indicate misspelled words. This can result in a 'cluttered' look which can make these fields more difficult to read.  HTML5 standard has a 'spellcheck' attribute (https://html.spec.whatwg.org/#attr-spellcheck), which can be set to 'false' to disable the spellcheck on a per element basis.

I would recommend that at minimum, the fields that have been converted to monospace should also have spellcheck disabled.  Very few fields in zabbix would seem to be appropriate for spellchecking.