[improvement] Picker: update style (#1887)

packages/vant-css/src/picker.css

@@ -9,8 +9,8 @@
 
   &__toolbar {
     display: flex;
-    height: 40px;
-    line-height: 40px;
+    height: 44px;
+    line-height: 44px;
     justify-content: space-between;
   }
 
@@ -18,6 +18,7 @@
   &__confirm {
     color: $blue;
     padding: 0 15px;
+    font-size: 14px;
 
     &:active {
       background-color: $active-color;
@@ -26,6 +27,8 @@
 
   &__title {
     max-width: 50%;
+    font-size: 16px;
+    font-weight: 500;
     text-align: center;
   }
 
@@ -70,7 +73,8 @@
       color: $gray-dark;
 
       &--selected {
-        color: $black;
+        font-weight: 500;
+        color: $text-color;
       }
 
       &--disabled {