get screen width using php in template

[prince]

hello master of mybb and spacial php masters..

i am already use Template Conditionals mybb plugin and try to make
<if content usign screen width but its'nt work properly.

PHP Code:

<if window.screen.width <= 680 then> You are using mobile device</if> <if window.screen.width >= 680 then> You are using computer</if>

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but itsn't work please fix this issue.