Android v21 Theme.Appcompat color accent is ignored, no padding on dialogs

About the accent color. You are using a AppCompat theme so you should remove Android from the namespace inside your theme.

<style name="AppTheme_Light" parent="Theme.AppCompat.Light.DarkActionBar">
    <item name="colorPrimary">@color/abc1</item>
    <item name="colorPrimaryDark">@color/abc2</item>
    <item name="colorAccent">@color/abc3</item>
</style>

About the dialog. AppCompat doesn’t support it (as I know).
You can try to use this style in your values-v21 folder:

<style name="Theme" parent="FrameworkRoot.Theme">
    <item name="android:alertDialogTheme">@style/Theme.AlertDialog</item>
</style>

<style name="Theme.AlertDialog" parent="android:Theme.Material.Light.Dialog.Alert">
    <item name="android:colorPrimary">@color/demo_primary_color</item>
    <item name="android:colorPrimaryDark">@color/demo_colorPrimaryDark</item>
    <item name="android:colorAccent">@color/theme_accent_1</item>
</style>

UPDATE 23/04/2015: SUPPORT LIBRARY V.22.1

The new support library v22.1 works with the Dialog.
You can use an android.support.v7.app.AlertDialog or the new AppCompatDialog.

For example:

import android.support.v7.app.AlertDialog

AlertDialog.Builder builder =
       new AlertDialog.Builder(this, R.style.AppCompatAlertDialogStyle);
            builder.setTitle("Dialog");
            builder.setMessage("Lorem ipsum dolor ....");
            builder.setPositiveButton("OK", null);
            builder.setNegativeButton("Cancel", null);
            builder.show();

And use a style like this:

<style name="AppCompatAlertDialogStyle" parent="Theme.AppCompat.Light.Dialog.Alert">
    <item name="colorAccent">#FFCC00</item>
    <item name="android:textColorPrimary">#FFFFFF</item>
    <item name="android:background">#5fa3d0</item>
</style>

Otherwise you can define in your current theme:

<style name="AppTheme" parent="Theme.AppCompat.Light">
    <!-- your style -->
    <item name="alertDialogTheme">@style/AppCompatAlertDialogStyle</item>
</style>

and then in your code:

 import android.support.v7.app.AlertDialog

    AlertDialog.Builder builder =
           new AlertDialog.Builder(this);