Popup resizing issues

I'm having an issue getting popups to resize at all. I can change the width, but I get a scrollbar instantly that makes the height 90% of the page:



..and if I then try to resize the height of the popup, it ignores me except to move the scrollbar further in:




Here's my XML:

<skuidpage unsavedchangeswarning="yes" personalizationmode="server" showsidebar="true" useviewportmeta="true" showheader="true">
    <models/>
    <components>
        <pagetitle uniqueid="sk-34oC-235">
            <maintitle>
                <template>{{Name}}</template>
            </maintitle>
            <subtitle>
                <template>{{Model.label}}</template>
            </subtitle>
            <actions>
                <action type="popup" label="New Button" uniqueid="sk-34oD-240">
                    <popup title="New Popup" width="10%">
                        <components>
                            <richtext multiple="false" uniqueid="sk-34oF-252">
                                <contents>&lt;p&gt;&lt;strong&gt;WORDS&lt;/strong&gt;&lt;/p&gt;
</contents>
                            </richtext>
                        </components>
                        <afterclose/>
                    </popup>
                    <hotkeys/>
                    <renderconditions logictype="and"/>
                    <enableconditions/>
                </action>
            </actions>
        </pagetitle>
    </components>
    <resources>
        <labels/>
        <javascript/>
        <css/>
        <actionsequences/>
    </resources>
    <styles>
        <styleitem type="background" bgtype="none"/>
    </styles>
    <interactions/>
</skuidpage>



I'm even using the "Default" theme that I haven't touched. Any ideas what might be the issue? I tried with both the latest version of Firefox (62.0) and a newer version of Chrome (68.0.3440.106) and both behave very similarly.

Thanks!