I have added some css classes to your code in order.php, maybe handy to change in future release. Its extremely simple to add, and this way you can do various custom css changes:
changed:
<div class="aligncenter" style="width:45%">
to:
<div class="aligncenter btc-block" style="width:45%">
To be able to add margins, paddings, height to the whole block.
changed:
<div class="" style="margin-bottom:10px;" >
<h3 ng-show="order.status == -1" ng-cloak >To pay, send exact amount of BTC to the given address</h3>
to:
<div class="btc-txt" style="margin-bottom:10px;" >
<h3 ng-show="order.status == -1" ng-cloak >To pay, send exact amount of BTC to the given address</h3>
To be able to change the h3 and span text settings.
changed:
<table class="">
to:
<table class="btc-table">
To be able to change the h5 settings and other table options.
changed:
<td class="" style="vertical-align:top;">
<h5 for="invoice-amount">Amount</h5>
to:
<td class="btc-amount" style="vertical-align:top;">
<h5 for="invoice-amount">Amount</h5>
To be able to change the amount settings.
changed:
<input type="text" class="" ng-value="order.address" readonly="readonly">
to:
<input type="text" class="btc-address" ng-value="order.address" readonly="readonly">
To be able to change the btc address settings.
If you take a bit more time you can probably optimize it a bit, maybe even add some options in wp-admin so you can set all settings there. But with above code you can simply change all colors, heights, width, paddings and margins with some simple custom css codes in your theme.