Fix oppia#2620 : Fix exploration card height and deadzone (oppia#2971)

* Remove deadzone and hardcoded height

* fix card's hardcoded height and deadzone

* restore card title margin

* fixing card title margin

* fix margin of title

* fix the noticable difference between title and objective

core/templates/dev/head/css/oppia.css

@@ -3650,7 +3650,7 @@ md-card.preview-conversation-skin-supplemental-card {
   background-color: #fff;
   cursor: pointer;
   display: inline-block;
-  height: 258px;
+  height: inherit;
   /*
     The margin setting is so that exploration summary tiles and collection
     summary tiles would be the same widths (214px).
@@ -3718,7 +3718,7 @@ md-card.preview-conversation-skin-supplemental-card {
 }
 
 .oppia-activity-summary-tile .title-section {
-  height: 162px;
+  height: 10em;
   position: relative;
   width: 100%;
 }
@@ -3835,9 +3835,10 @@ md-card.preview-conversation-skin-supplemental-card {
   font-size: 1em;
   font-weight: normal;
   line-height: 1.2em;
-  margin: 12px;
-  padding: 0;
+  margin: 0.3em 0.5em;
+  padding: 0.2em;
   position: absolute;
+  word-break: break-all;
 }
 
 .oppia-activity-summary-tile .objective {
@@ -3887,7 +3888,7 @@ md-card.preview-conversation-skin-supplemental-card {
 
 .oppia-dashboard-statistics-card-link {
   background: white;
-  height: 88px;
+  height: 25.5%;
   opacity: 0;
   position: absolute;
   width: 184px;
@@ -3925,7 +3926,7 @@ md-card.preview-conversation-skin-supplemental-card {
 }
 
 .oppia-dashboard-card-view-item {
-  height: 250px;
+  height: inherit;
   margin-left: 7.5px;
   margin-right: 7.5px;
   position: static;
@@ -3940,7 +3941,8 @@ md-card.preview-conversation-skin-supplemental-card {
 
 .oppia-dashboard-card-view-item .exp-private-text {
   font-size: 13px;
-  margin: 13px 11px 0;
+  margin: 0 0.5em;
+  padding: 0.2em; 
 }
 
 .oppia-dashboard-card-view-item .metrics {