fix css

packages/artplayer/src/style/bottom.less

@@ -38,6 +38,7 @@
                     position: relative;
                     height: 50%;
                     width: 100%;
+                    transition: all 0.2s ease;
                     background: rgba(255, 255, 255, 0.2);
 
                     .art-progress-loaded {