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                <div class="container">
  <div class="outer">
    <div class="inner">
      <div class="block">бокс</div>


                /*Setup Environment */
html                 { box-sizing: border-box; }
*, *:before, *:after { box-sizing: inherit; }
body                 { font-family: Verdana, Arial, Helvetica, sans-serif; font-size:16px; margin:0; padding:0; }

.block               { display:inline-block; background-color:#999999; color:#000000; font-size:0.8em; text-align:center; line-height:4em; padding:10px;}

Calc Demo 100% Fluid Width using negative margins
In This scenario, we have markup for a parent container that has a negative margin.

We want the child element, for styling reasons, to sit flush left in this particular scenario and still be 100% width.

When a negative margin is applied, if you were to declare 100% width on the child element this will be 10px out (due to the negative margin), so we can rectify by using calc.


.container{ margin:100px auto 0 auto; width:80%; border:1px dashed red; }
.outer    { display:inline-block; width:100%; padding:10px; }
.inner    { display:inline-block; width:100%; margin-left:-10px; }

/*Block is now 100% fluid width of the container and respects the top, right and bottom padding */
.block    {  width: calc(100% + 10px); }