diff --git a/flexiui-core/build.gradle.kts b/flexiui-core/build.gradle.kts
index 6633faf..33cb254 100644
--- a/flexiui-core/build.gradle.kts
+++ b/flexiui-core/build.gradle.kts
@@ -25,6 +25,7 @@ kotlin {
     sourceSets {
         all {
             languageSettings {
+                optIn("com.highcapable.flexiui.ExperimentalFlexiUISizesApi")
                 optIn("androidx.compose.ui.ExperimentalComposeUiApi")
                 optIn("androidx.compose.foundation.ExperimentalFoundationApi")
             }
diff --git a/flexiui-core/src/commonMain/kotlin/com/highcapable/flexiui/Sizes.kt b/flexiui-core/src/commonMain/kotlin/com/highcapable/flexiui/Sizes.kt
index 354b808..6118e7d 100644
--- a/flexiui-core/src/commonMain/kotlin/com/highcapable/flexiui/Sizes.kt
+++ b/flexiui-core/src/commonMain/kotlin/com/highcapable/flexiui/Sizes.kt
@@ -28,8 +28,7 @@ import androidx.compose.runtime.staticCompositionLocalOf
 import androidx.compose.ui.unit.Dp
 import androidx.compose.ui.unit.dp
 
-// TODO: Some sizes will modify in the future
-
+@ExperimentalFlexiUISizesApi
 @Immutable
 data class Sizes(
     val spacingPrimary: Dp,
@@ -61,4 +60,18 @@ internal val DefaultSizes = Sizes(
     borderSizePrimary = 2.dp,
     borderSizeSecondary = 1.dp,
     borderSizeTertiary = 0.dp
-)
\ No newline at end of file
+)
+
+/**
+ * The [Sizes] is experimental, the relevant design specifications for size are still being improved,
+ * this is the old design plan.
+ *
+ * Some sizes will modify in the future.
+ */
+@RequiresOptIn(
+    message = "The Sizes is experimental, the relevant design specifications for size are still being improved, this is the old design plan.\n" +
+        "Some sizes will modify in the future.",
+    level = RequiresOptIn.Level.WARNING
+)
+@MustBeDocumented
+annotation class ExperimentalFlexiUISizesApi
\ No newline at end of file