[Improvement] uniform fade animation (#410)

packages/vant-css/src/common/animation.css

@@ -19,6 +19,25 @@
   }
 }
 
+@keyframes van-fade-out {
+  from {
+    opacity: 1;
+  }
+  to {
+    opacity: 0;
+  }
+}
+
+.van-fade {
+  &-enter-active {
+    animation: .3s van-fade-in;
+  }
+
+  &-leave-active {
+    animation: .3s van-fade-out;
+  }
+}
+
 .van-slide-bottom {
   &-enter-active {
     animation: van-slide-bottom-enter .3s both ease;

packages/vant-css/src/popup.css

@@ -8,7 +8,6 @@
     top: 0;
     left: 0;
     background-color: rgba(0, 0, 0, 0.7);
-    animation: van-fade-in .3s both;
   }
 
   &-overflow-hidden {
@@ -77,7 +76,3 @@
 .popup-slide-left-enter, .popup-slide-left-leave-active {
   transform: translate3d(-100%, -50%, 0);
 }
-
-.popup-fade-enter, .popup-fade-leave-active {
-  opacity: 0;
-}

packages/vant-css/src/toast.css

@@ -17,10 +17,6 @@
   transform: translate3d(-50%, -50%, 0);
   background-color: rgba(39, 39, 39, .7);
 
-  &-wrapper {
-    transition: opacity .2s;
-  }
-
   &__overlay {
     position: fixed;
     top: 0;
@@ -68,7 +64,3 @@
     bottom: 50px;
   }
 }
-
-.van-toast-fade-enter, .van-toast-fade-leave-to {
-  opacity: 0;
-}