Re-added already existing base for less backwards compatability.

IPython/html/static/base/less/flexbox.less

@@ -81,7 +81,8 @@ Browsers not listed, including Safari, are supported via the styling under the
 }
 
 .hbox.reverse,
-.vbox.reverse {
+.vbox.reverse,
+.reverse {
     /* Old browsers */
     -webkit-box-direction: reverse;
     -moz-box-direction: reverse;
@@ -92,7 +93,8 @@ Browsers not listed, including Safari, are supported via the styling under the
 }
 
 .hbox.box-flex0,
-.vbox.box-flex0 {
+.vbox.box-flex0,
+.box-flex0 {
     /* Old browsers */
     -webkit-box-flex: 0;
     -moz-box-flex: 0;
@@ -104,7 +106,8 @@ Browsers not listed, including Safari, are supported via the styling under the
 }
 
 .hbox.box-flex1,
-.vbox.box-flex1 {
+.vbox.box-flex1,
+.box-flex1 {
     /* Old browsers */
     -webkit-box-flex: 1;
     -moz-box-flex: 1;
@@ -115,13 +118,15 @@ Browsers not listed, including Safari, are supported via the styling under the
 }
 
 .hbox.box-flex,
-.vbox.box-flex {
+.vbox.box-flex,
+.box-flex {
     /* Old browsers */
     .box-flex1();
 }
 
 .hbox.box-flex2,
-.vbox.box-flex2 {
+.vbox.box-flex2,
+.box-flex2 {
     /* Old browsers */
     -webkit-box-flex: 2;
     -moz-box-flex: 2;
@@ -146,7 +151,8 @@ Browsers not listed, including Safari, are supported via the styling under the
 }
 
 .hbox.start, 
-.vbox.start {
+.vbox.start,
+.start {
     /* Old browsers */
     -webkit-box-pack: start;
     -moz-box-pack: start;
@@ -157,7 +163,8 @@ Browsers not listed, including Safari, are supported via the styling under the
 }
 
 .hbox.end, 
-.vbox.end {
+.vbox.end,
+.end {
     /* Old browsers */
     -webkit-box-pack: end;
     -moz-box-pack: end;
@@ -168,7 +175,8 @@ Browsers not listed, including Safari, are supported via the styling under the
 }
 
 .hbox.center, 
-.vbox.center {
+.vbox.center,
+.center {
     /* Old browsers */
     -webkit-box-pack: center;
     -moz-box-pack: center;
@@ -179,7 +187,8 @@ Browsers not listed, including Safari, are supported via the styling under the
 }
 
 .hbox.align-start, 
-.vbox.align-start {
+.vbox.align-start,
+.align-start {
     /* Old browsers */
     -webkit-box-align: start;
     -moz-box-align: start;
@@ -190,7 +199,8 @@ Browsers not listed, including Safari, are supported via the styling under the
 }
 
 .hbox.align-end, 
-.vbox.align-end {
+.vbox.align-end,
+.align-end {
     /* Old browsers */
     -webkit-box-align: end;
     -moz-box-align: end;
@@ -201,7 +211,8 @@ Browsers not listed, including Safari, are supported via the styling under the
 }
 
 .hbox.align-center, 
-.vbox.align-center {
+.vbox.align-center,
+.align-center {
     /* Old browsers */
     -webkit-box-align: center;
     -moz-box-align: center;