That widget is #widget_366. CSS applied to #widget_43 will only affect that widget and no others. If you have multiple Ad Modules, you will have to have code for each one if you want to go the specific route.
Each ID like #widget_366 can only exist on the page once. Every single widget on your site will have its own unique ID. You need to inspect them in the browser to see what your Widget is designated as.
You should be able to target all Ad Widgets with CSS like:
[data-widget-id='43'] .widget-header {CSS CODE HERE}
Code:
<div class="b-module js-module canvas-widget default-widget axd-widget axd-container" id="widget_366" data-widget-id="43" data-widget-instance-id="366"> <div class="widget-header h-clearfix"> <div class="module-title h-left"> <h1 class="main-title js-main-title hide-on-editmode">FORUM SPONSORS</h1> </div> <div class="module-buttons"> <span class="toggle-button module-button-item collapse" title="Collapse" data-toggle-title="Expand"><span class="b-icon b-icon__toggle-collapse">Collapse</span></span> </div> </div> <div class="widget-content restore axd axd_366"> <div class="axd-inner js-module__hide-if-empty "> <div class="ad_366_inner"><a href="https://www.amsoil.com/offers/index.aspx/?zo=1907169"><img src="core/css/0/0/3/4/5/5//images/Amsoil 320.jpg"></a></div> </div> </div> </div>
You should be able to target all Ad Widgets with CSS like:
[data-widget-id='43'] .widget-header {CSS CODE HERE}
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