Position down all the scroll in ionic 3 - css

Question

I'm creating a chat and my problem is that the div that has the messages inside it I put a scroll, but I can not keep it under everything.
This is the view code and styles:
<ion-grid>
<ion-row>
<ion-col col-12>
<button ion-button block color="success" style="text-transform: none" (click)="seeMembers()">See members</button>
</ion-col>
<ion-col col-12 class="div_chat" #div_theme>
<ion-list insert>
<button ion-item>
<p>test</p>
<p>test</p><p>test</p><p>test</p><p>test</p><p>test</p><p>test</p><p>test</p><p>test</p><p>test</p><p>test</p><p>test</p><p>test</p><p>test</p><p>test</p><p>test</p><p>test</p><p>test</p><p>test</p><p>test</p><p>test</p><p>test</p><p>test</p><p>test</p>
</button>
</ion-list>
<h3 *ngIf="themeDB == false" text-center><strong>There are no new Topics</strong></h3>
</ion-col>
</ion-row>
</ion-grid>
This is my stylesheet
page-see-theme{
.div_chat{
width: 100%;
height: 300px;
overflow-y: auto;
}
}
Any idea is very useful, thanks for your help