magento 2 slider as well as mageplaza banner slider won't show in my custom theme

Question

I had installed mageplaza banner slider followed their guide. but the slider wont show in my custom theme. this happen as well with the default magento 2 slider

Answer 1

the problem was in the css file when I change the direction of the contents from right to left (the page is in Arabic)

body{
  direction: rtl !important;
}

if comment this part of code

body{
  //direction: rtl !important;
}

the problem got fixed. but Iam not sure what is the cause.