The HTML (only the affected panel) looks like that.
<!-- WATERMARK -->
<div id="outercontainer_watermark">
<div class="label_category"><span data-key="pnl_watermark">Watermark</span><sp-checkbox id="input_watermarkenabled" checked></sp-checkbox></div>
<div id="panel_watermark" class="panel_category stripes">
<div class="panel_row">
<div style="display: flex; flex-flow: row; flex: 1;">
<sp-button id="button_watermarkfile" class="filebutton" quiet variant="secondary" nofocus>
<svg xmlns="http://www.w3.org/2000/svg" height="18" viewBox="0 0 18 18" width="18">
<!-- <defs><style>.a {fill: #6E6E6E;}</style></defs> -->
<!-- <title>S Search 18 N</title> -->
<rect id="Canvas" fill="#ff13dc" opacity="0" width="18" height="18" /><path class="a" d="M16.5865,15.107,12.7,11.2215A6.413,6.413,0,1,0,11.2215,12.7l3.886,3.886a1.05,1.05,0,0,0,1.479-1.479ZM3,7.5A4.5,4.5,0,1,1,7.5,12,4.5,4.5,0,0,1,3,7.5Z" />
</svg>
</sp-button>
<sp-textfield id="input_watermarkfile" placeholder="" style="flex: 1 auto;" readonly textfieldfix><option id="token_watermarkfile" value=""></option></sp-textfield>
<sp-button class="clearbutton" quiet variant="secondary" nofocus>
<svg xmlns="http://www.w3.org/2000/svg" height="18" viewBox="0 0 18 18" width="18">
<!-- <defs><style>.a {fill: #6E6E6E;}</style></defs> -->
<!-- <title>S Close 18 N</title> -->
<rect id="Canvas" fill="#ff13dc" opacity="0" width="18" height="18" /><path class="a" d="M13.2425,3.343,9,7.586,4.7575,3.343a.5.5,0,0,0-.707,0L3.343,4.05a.5.5,0,0,0,0,.707L7.586,9,3.343,13.2425a.5.5,0,0,0,0,.707l.707.7075a.5.5,0,0,0,.707,0L9,10.414l4.2425,4.243a.5.5,0,0,0,.707,0l.7075-.707a.5.5,0,0,0,0-.707L10.414,9l4.243-4.2425a.5.5,0,0,0,0-.707L13.95,3.343a.5.5,0,0,0-.70711-.00039Z" />
</svg>
</sp-button>
</div>
</div>
<div class="panel_row">
<div style="display: flex; flex-flow: column; flex: 1 auto;">
<div style="display: flex; flex-flow: row nowrap; flex: 1 auto; margin: 2px 0px 12px 0px;">
<sp-label class="label_slider" data-key="lbl_watermarkopacity">Watermark Opacity:</sp-label>
<sp-slider class="valueslider" style="flex: 1 auto;" variant="filled" min="0" max="100" value="100" step="5"></sp-slider>
<sp-textfield id="input_watermarkopacity" type="number" class="slidervalue" value="100" style="flex: 0 0 60px; margin-left: 6px; text-align: center;"></sp-textfield>
</div>
<div style="display: flex; flex-flow: row nowrap; flex: 1 auto;">
<sp-label class="label_slider" data-key="lbl_watermarkborder">Border (px):</sp-label>
<sp-slider class="valueslider" style="flex: 1 auto;" variant="filled" min="0" max="100" value="0" step="5"></sp-slider>
<sp-textfield id="input_watermarkborder" type="number" class="slidervalue" value="0" style="flex: 0 0 60px; margin-left: 6px; text-align: center;"></sp-textfield>
</div>
</div>
<sp-radio-group id="input_watermarkposition">
<sp-radio value="wmposition_tl"></sp-radio>
<sp-radio value="wmposition_tm"></sp-radio>
<sp-radio value="wmposition_tr"></sp-radio>
<sp-radio value="wmposition_ml"></sp-radio>
<sp-radio value="wmposition_mm"></sp-radio>
<sp-radio value="wmposition_mr"></sp-radio>
<sp-radio value="wmposition_bl"></sp-radio>
<sp-radio value="wmposition_bm"></sp-radio>
<sp-radio value="wmposition_br" checked></sp-radio>
</sp-radio-group>
</div>
</div>
</div>
And here is the relevant excerpt from the CSS file.
div.label_category {
display: inline-flex;
position: relative;
top: +10px;
left: 8px;
height: 27px;
padding: 0px 12px;
border-radius: 6px;
z-index: 1000;
background-color: #756f67;
margin: 0;
color: white;
}
div.label_category span {
padding: 3px 0px !important;
}
div.label_category sp-checkbox {
display: inline-block;
height: 24px;
}
sp-radio-group#input_watermarkposition {
border: 2px solid #756f67;
border-radius: 6px;
display: flex;
flex-flow: row wrap;
flex: 0 78px;
padding: 0px;
margin-left: 24px;
}
sp-radio-group#input_watermarkposition sp-radio {
width: 14px ;
height: 14px;
/*padding: 2px 0px 0px 1px;*/
margin: 5px;
background-color: red;
}