Missing styling utilities for Status Page

There is a couple of styling utilities required for styling Status Page but missing in @gitab/ui utilities. This issue is to aggregate all missing styles so that they can be eventually added as utility classes, mixins, variables in @giltab/ui project and removed from Status Page project

• Markdown styles
• y-margin equivalent to 40px and x-margin to 48px

.page-container {
  margin: 40px 48px;
}

• box-shadow mixin

@mixin gl-inset-border-b-1-gray-200 {
  box-shadow: inset 0 ($gl-border-size-1 * -1) 0 0 $gray-200;
}

.gl-inset-border-b-1-gray-200 {
  @include gl-inset-border-b-1-gray-200;
}

• .gl-my-7 (32px)

@mixin gl-my-7 {
  margin-top: $gl-spacing-scale-7;
  margin-bottom: $gl-spacing-scale-7;
}

h2 {
  @include gl-my-7;
}