Fix specifity of flex modifier classes

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

@@ -80,7 +80,8 Browsers not listed, including Safari, are supported via the styling under the
     flex: none;
 }
 
-.reverse {
+.hbox.reverse,
+.vbox.reverse {
     /* Old browsers */
     -webkit-box-direction: reverse;
     -moz-box-direction: reverse;
@@ -90,7 +91,8 Browsers not listed, including Safari, are supported via the styling under the
     flex-direction: row-reverse;
 }
 
-.box-flex0 {
+.hbox.box-flex0,
+.vbox.box-flex0 {
     /* Old browsers */
     -webkit-box-flex: 0;
     -moz-box-flex: 0;
@@ -101,7 +103,8 Browsers not listed, including Safari, are supported via the styling under the
     width: auto;
 }
 
-.box-flex1 {
+.hbox.box-flex1,
+.vbox.box-flex1 {
     /* Old browsers */
     -webkit-box-flex: 1;
     -moz-box-flex: 1;
@@ -111,12 +114,14 Browsers not listed, including Safari, are supported via the styling under the
     flex: 1;
 }
 
-.box-flex {
+.hbox.box-flex,
+.vbox.box-flex {
     /* Old browsers */
     .box-flex1();
 }
 
-.box-flex2 {
+.hbox.box-flex2,
+.vbox.box-flex2 {
     /* Old browsers */
     -webkit-box-flex: 2;
     -moz-box-flex: 2;
@@ -140,7 +145,8 Browsers not listed, including Safari, are supported via the styling under the
     box-flex-group: 2;
 }
 
-.start {
+.hbox.start, 
+.vbox.start {
     /* Old browsers */
     -webkit-box-pack: start;
     -moz-box-pack: start;
@@ -150,7 +156,8 Browsers not listed, including Safari, are supported via the styling under the
     justify-content: flex-start;
 }
 
-.end {
+.hbox.end, 
+.vbox.end {
     /* Old browsers */
     -webkit-box-pack: end;
     -moz-box-pack: end;
@@ -160,7 +167,8 Browsers not listed, including Safari, are supported via the styling under the
     justify-content: flex-end;
 }
 
-.center {
+.hbox.center, 
+.vbox.center {
     /* Old browsers */
     -webkit-box-pack: center;
     -moz-box-pack: center;
@@ -170,7 +178,8 Browsers not listed, including Safari, are supported via the styling under the
     justify-content: center;
 }
 
-.align-start {
+.hbox.align-start, 
+.vbox.align-start {
     /* Old browsers */
     -webkit-box-align: start;
     -moz-box-align: start;
@@ -180,7 +189,8 Browsers not listed, including Safari, are supported via the styling under the
     align-items: flex-start;
 }
 
-.align-end {
+.hbox.align-end, 
+.vbox.align-end {
     /* Old browsers */
     -webkit-box-align: end;
     -moz-box-align: end;
@@ -190,7 +200,8 Browsers not listed, including Safari, are supported via the styling under the
     align-items: flex-end;
 }
 
-.align-center {
+.hbox.align-center, 
+.vbox.align-center {
     /* Old browsers */
     -webkit-box-align: center;
     -moz-box-align: center;