Bootstrap Theme: Not working on mobile devices

My bootstrap theme isn't displayed correctly on mobile devices, but on desktop computers it works just fine when you adjust the size of the browserwindow to small screensizes.
On every mobile device the size of the screen-width seems fixed to 980 pixels and I don't know why.

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jordif replied on at Permalink Reply

it seems you forgot to add this line in the header of your concrete5 theme:

<meta name="viewport" content="width=device-width, initial-scale=1">

Try adding that line and see if that fixes it.

conker39 replied on at Permalink Reply
Thank you Mr. Robot, you made my day :)

I was totally convinced that Concrete5 would fill in the viewport-code. Sometimes you don't see the forest for the trees.