wp-calypso/client/signup/steps/social-profiles/style.scss

@import "@wordpress/base-styles/breakpoints";
@import "@wordpress/base-styles/mixins";

.signup__step .is-social-profiles {
	.step-wrapper__header {
		@include break-small {
			flex-basis: 40%;
		}
	}

	.step-wrapper__content {
		@include break-small {
			flex-basis: 50%;
		}
	}

	.step-wrapper.is-horizontal-layout {
		@include break-small {
			margin-top: 15vh;
		}
	}
}