Content width

On wide monitors content is 840px wide. Im trying to change it to 1000px at least. I tried to add this

.entry-content{
    width:1170px;
    margin-left:auto !important;
    margin-right:auto !important;
}

And it works on wide monitors but on mobile phones and tablets content is a mess (hudge black magin on right). Width isnt given stright in this theme so im trying to find paddings and margins one by one. But still no luck