Tables like the Overview table under Monitoring have their table headers text aligned vertically.

This is achieved by using something called a CSS writing mode.

In Zabbix 2.4.7 apparently the type of writing mode used is called "tb-rl".
This particular writing mode is deprecated and since the last Google Chrome update results in horizontal text in stead of vertical text. This screws up the table header.

Simply changing the writing mode from "tb-rl" to "vertical-rl" in the CSS file(s) should fix the issue.