design-themes/theme_nano/views/customize_modal.xml

<?xml version="1.0" encoding="utf-8"?>
<odoo>
    <template id="customize_modal" inherit_id="theme_common.theme_customize">
        <!-- Set number of fonts -->
        <xpath expr="//t[@t-set='_nb_fonts']" position="attributes">
            <attribute name="t-value">11</attribute>
        </xpath>

        <xpath expr="//content[@id='theme_customize_content_layout']/*" position="before">
            <list string="Menu">
                <opt string="Standard" data-xmlid=""/>
                <opt string="Side Navigation" data-xmlid="theme_nano.option_side_nav_variables, website.no_autohide_menu"/>
            </list>
            <list string="Icons Bar">
                <opt id="option_icons_bar_show" string="Show" data-xmlid=""/>
                <opt string="Hide" data-xmlid="theme_nano.option_icons_sidebar_none_variables"/>
            </list>
            <list string="Icons Bar Position" data-depends="option_icons_bar_show">
                <opt string="Left" data-xmlid=""/>
                <opt string="Right" data-xmlid="theme_nano.option_icons_sidebar_right"/>
            </list>
        </xpath>
    </template>

    <!-- Layouts -->
    <template id="option_side_nav_variables" inherit_id="theme_nano._assets_primary_variables" active="True">
        <xpath expr="//link[last()]" position="after">
            <link rel="stylesheet" type="text/scss" href="/theme_nano/static/src/scss/options/layouts/side_nav_variables.scss"/>
        </xpath>
    </template>
    <template id="option_icons_sidebar_right" inherit_id="theme_nano.option_side_nav_variables" active="False">
        <xpath expr="//link[last()]" position="after">
            <link rel="stylesheet" type="text/scss" href="/theme_nano/static/src/scss/options/layouts/icons_sidebar_right.scss"/>
        </xpath>
    </template>
    <template id="option_icons_sidebar_none_variables" inherit_id="theme_nano.option_side_nav_variables" active="False">
        <xpath expr="//link[last()]" position="after">
            <link rel="stylesheet" type="text/scss" href="/theme_nano/static/src/scss/options/layouts/icons_sidebar_none_variables.scss"/>
        </xpath>
    </template>
</odoo>