Backport PR #7718: Disable output contents from overflowing page width.

A scrollbar will appear when the output is too wide.

closes  #7701
alternative to  #7721

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

@@ -94,6 +94,8 b' div.output_area pre {'
 /* This class is for the output subarea inside the output_area and after
    the prompt div. */
 div.output_subarea {
+    // Don't let contents overflow page area.
+    overflow-x: auto;
     padding: @code_padding;
     .box-flex1();
 }

IPython/html/static/style/ipython.min.css

@@ -873,6 +873,7 b' div.output_area pre {'
 /* This class is for the output subarea inside the output_area and after
    the prompt div. */
 div.output_subarea {
+  overflow-x: auto;
   padding: 0.4em;
   /* Old browsers */
   -webkit-box-flex: 1;

IPython/html/static/style/style.min.css

@@ -9665,6 +9665,7 b' div.output_area pre {'
 /* This class is for the output subarea inside the output_area and after
    the prompt div. */
 div.output_subarea {
+  overflow-x: auto;
   padding: 0.4em;
   /* Old browsers */
   -webkit-box-flex: 1;