output_scroll can't be a vbox.

IPython/html/static/notebook/less/outputarea.less

@@ -1,166 +1,167 b''
 div.output_wrapper {
     /* this position must be relative to enable descendents to be absolute within it */
     position: relative;
     .vbox()
 }
 
 /* class for the output area when it should be height-limited */
 div.output_scroll {
     /* ideally, this would be max-height, but FF barfs all over that */
     height: 24em;
     /* FF needs this *and the wrapper* to specify full width, or it will shrinkwrap */
     width: 100%;
 
     overflow: auto;
     .corner-all;
     .box-shadow(inset 0 2px 8px rgba(0, 0, 0, .8));
+    display: block;
 }
 
 /* output div while it is collapsed */
 div.output_collapsed {
     margin: 0px;
     padding: 0px;
     .vbox();
 }
 
 div.out_prompt_overlay {
     height: 100%;
     padding: 0px @code_padding;
     position: absolute;
     .corner-all;
 }
 
 div.out_prompt_overlay:hover {
     /* use inner shadow to get border that is computed the same on WebKit/FF */
     .box-shadow(inset 0 0 1px #000);
     background: rgba(240, 240, 240, 0.5);
 }
 
 div.output_prompt {
     color: darkred;
 }
 
 /* This class is the outer container of all output sections. */
 div.output_area {
     padding: 0px;
     page-break-inside: avoid;
     .hbox();
 
     .MathJax_Display {
         // Inside a CodeCell, elements are left justified
         text-align: left !important;
     }
 
     .rendered_html {
         // Inside a CodeCell, elements are left justified
         table {
             margin-left: 0;
             margin-right: 0;
         }
     
         img {
             margin-left: 0;
             margin-right: 0;
         }
     }
 }
 
 /* This is needed to protect the pre formating from global settings such
    as that of bootstrap */
 .output {
     .vbox();
 }
 
 div.output_area pre {   
     font-family: @monoFontFamily;
     margin: 0;
     padding: 0;
     border: 0;
     font-size: 100%;
     vertical-align: baseline;
     color: black;
     background-color: transparent;
     .border-radius(0);
     line-height: inherit;
 }
 
 /* This class is for the output subarea inside the output_area and after
    the prompt div. */
 div.output_subarea {
     padding: @code_padding @code_padding 0.0em @code_padding;
     .box-flex1();
 }
 
 /* The rest of the output_* classes are for special styling of the different
    output types */
 
 /* all text output has this class: */
 div.output_text {
     text-align: left;
     color: @textColor;
     font-family: @monoFontFamily;
     /* This has to match that of the the CodeMirror class line-height below */  
     line-height: @code_line_height;
 }
 
 /* stdout/stderr are 'text' as well as 'stream', but pyout/pyerr are *not* streams */
 div.output_stream {
 }
 
 div.output_stdout {
 }
 
 div.output_stderr {
     background: #fdd; /* very light red background for stderr */
 }
 
 div.output_latex {
     text-align: left;
 }
 
 div.output_html {
 }
 
 div.output_png {
 }
 
 div.output_jpeg {
 }
 
 /* Empty output_javascript divs should have no height */
 div.output_javascript:empty {
     padding: 0;
 }
 
 .js-error {
     color: darkred;
 }
 
 /* raw_input styles */
 
 div.raw_input {
     padding-top: 0px;
     padding-bottom: 0px;
     height: 1em;
     line-height: 1em;
     font-family: @monoFontFamily;
 }
 
 span.input_prompt {
     font-family: inherit;
 }
 
 input.raw_input {
     font-family: inherit;
     font-size: inherit;
     color: inherit;
     width: auto;
     margin: -2px 0px 0px 1px;
     padding-left: 1px;
     padding-top: 2px;
     height: 1em;
 }
 
 p.p-space {
     margin-bottom: 10px;
 }