Hello,

The post grid is a Visual Composer element that doesn’t get overwritten by theme style.
I can suggest adding this custom css into your Custom Css box to align the gray background. But aligning the “Read more” button can not be done using css only.

.vc_gitem-zone.vc_gitem-zone-c.vc_custom_1419240516480 {
    min-height: 475px !important;
}

I suggest you try adding the same amount of excerpt text in order to have the posts as aligned as possible.

Best regards!