ColorPicker: declare box-sizing for panel (#9780)

in case some users declare `box-sizing: border-box` globally and may causing unexpected problems

packages/theme-chalk/src/color-picker.scss

@@ -336,6 +336,7 @@
     position: absolute;
     z-index: 10;
     padding: 6px;
+    box-sizing: content-box;
     background-color: $--color-white;
     border: 1px solid $--border-color-lighter;
     border-radius: $--border-radius-base;