You can use the selector * , which applies to everything:
<style> * { font-family: Arial; } </style>
Please note that this may be redundant for your purposes - due to the nature of the CSS, the styles set on the parent elements are usually inherited by the child elements, and as a rule, this is enough to set the font style in the body element to apply to the whole page.
body { font-family: Arial; }
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