get screen width using php in template

[Ashan]

This user has been denied support.

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.

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

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

but itsn't work please fix this issue.