Hello Chris,

1) About css code:

You need to open your custom page via sturio -> pages builder and to create on it new RAW block, then select as Block Layout only Content and add the next code into the content of the block.

<style>

.bx-messenger-table-wrapper .bx-messenger-table-wrapper-rows {

    background-color: #fff;

}

.bx-messenger-table-wrapper div.bx-messenger-table-wrapper-rows:first-child .cell

{

    height:600px;

}

</style>

Done.

2) About online statuses: in history part of the messenger there is no statuses of the members, because they are shown in the left part of the main page. May be we need to think over it and to make visible statuses for history part also in case if it is independent block.