How to change selected option in <select> to shopify

Question

i have some select tags where is options and when i change option, my page refreshs and change url and i need to display what option is currently selected how to do it?

 <select
                name="brands"
                id="brands"
                onchange="FILTER.searchParams(event, 'filter.p.vendor')"
            >
              <option value="{{ collection.url }}">ALL</option>
              {% for product_vendor in collection.all_vendors %}
              <option {% if option.vendor == product_vendor %} selected="selected" {% endif %} >{{ product_vendor }}</option>
              {% endfor %}

            </select>
            <select
                name="category"
                id="category"
                onchange="FILTER.changePath(event)"
            >
              <option value="{{ collection.url }}">ALL</option>
              {% for collection in collections %}

              <option value="{{ collection.url }}">
                {{ collection.title  }} 
              </option>

              {% endfor %}
            </select>