Use attribute in content css
<style>
.paypal.before:before {
content: '- ' attr(data-label) ' -';
display: block;
margin: 10px 5px;
text-align: center;
text-transform: uppercase;
}
</style>
<div data-label="or" class="paypal checkout before paypal-logo ec_shortcut_c6446a6b290fa9af4fd6667d24fd5e51">
<input type="image" data-action="checkout-form-submit" data-checkout-url="/paypal/express/start/button/1/" src="https://fpdbs.sandbox.paypal.com/dynamicimageweb?cmd=_dynamic-image&buttontype=ecshortcut&locale=en_GB" alt="Checkout with PayPal" title="Checkout with PayPal">
</div>