feat(Popup): Provide option to handle vertical offset

        Completely inspired from Semantic-Org#1146 and its comments

src/modules/Popup/Popup.js

@@ -72,8 +72,11 @@ export default class Popup extends Component {
     /** Invert the colors of the Popup. */
     inverted: PropTypes.bool,
 
-    /** Horizontal offset in pixels to be applied to the Popup. */
-    offset: PropTypes.number,
+    /** Offset in pixels to be applied to the Popup. */
+    offset: PropTypes.oneOfType([
+      PropTypes.number,
+      PropTypes.arrayOf(PropTypes.number),
+    ]),
 
     /** Events triggering the popup. */
     on: PropTypes.oneOfType([
@@ -135,6 +138,7 @@ export default class Popup extends Component {
   static defaultProps = {
     position: 'top left',
     on: 'hover',
+    offset: 0,
   }
 
   static _meta = {
@@ -153,7 +157,6 @@ export default class Popup extends Component {
     // Do not access window/document when server side rendering
     if (!isBrowser()) return style
 
-    const { offset } = this.props
     const { pageYOffset, pageXOffset } = window
     const { clientWidth, clientHeight } = document.documentElement
 
@@ -188,15 +191,26 @@ export default class Popup extends Component {
       }
     }
 
-    if (offset) {
-      if (_.isNumber(style.right)) {
-        style.right -= offset
-      } else {
-        style.left -= offset
-      }
+    return { ...style, ...this.applyOffset(style) }
+  }
+
+  applyOffset = (style) => {
+    const { offset } = this.props
+    const [horizontal, vertical] = _.isNumber(offset) ? [offset, 0] : [...offset]
+    return {
+      ...this.applyHorizontalOffset(style, horizontal),
+      ...this.applyVeriticalOffset(style, vertical),
     }
+  }
+
+  applyVeriticalOffset = ({ top, bottom }, offset) => {
+    if (_.isNumber(top)) return { bottom, top: top + offset }
+    return { top, bottom: bottom + offset }
+  }
 
-    return style
+  applyHorizontalOffset = ({ right, left }, offset) => {
+    if (_.isNumber(right)) return { left, right: right + offset }
+    return { right, left: left + offset }
   }
 
   // check if the style would display

test/specs/modules/Popup/Popup-test.js

@@ -79,31 +79,78 @@ describe('Popup', () => {
     assertInBody('.ui.popup.visible.some-class')
   })
 
-  describe('offest', () => {
-    it('accepts an offest to the left', () => {
+  describe('offset', () => {
+    it('accepts an offset to the left', () => {
       wrapperMount(
         <Popup
-          offset={50}
-          position='bottom right'
+          offset={100}
+          position='bottom left'
+          content='foo'
+          trigger={<button>foo</button>}
+        />,
+      )
+
+      wrapper.find('button').simulate('click')
+
+      const rect = document.querySelector('.popup.ui').getBoundingClientRect()
+      const { left } = rect
+
+      expect(left).to.be.at.least(100)
+      assertInBody('.ui.popup.visible')
+    })
+    it('accepts an offset to the left', () => {
+      wrapperMount(
+        <Popup
+          offset={[100, 0]}
+          position='bottom left'
           content='foo'
           trigger={<button>foo</button>}
         />,
       )
 
       wrapper.find('button').simulate('click')
+
+      const rect = document.querySelector('.popup.ui').getBoundingClientRect()
+      const { left } = rect
+
+      expect(left).to.be.at.least(100)
       assertInBody('.ui.popup.visible')
     })
-    it('accepts an offest to the right', () => {
+    it('accepts an offset to the top', () => {
       wrapperMount(
         <Popup
-          offset={50}
+          offset={[0, 100]}
           position='bottom left'
           content='foo'
           trigger={<button>foo</button>}
         />,
       )
 
       wrapper.find('button').simulate('click')
+
+      const rect = document.querySelector('.popup.ui').getBoundingClientRect()
+      const { top } = rect
+
+      expect(top).to.be.at.least(100)
+      assertInBody('.ui.popup.visible')
+    })
+    it('accepts an offset to both top and left', () => {
+      wrapperMount(
+        <Popup
+          offset={[100, 100]}
+          position='bottom left'
+          content='foo'
+          trigger={<button>foo</button>}
+        />,
+      )
+
+      wrapper.find('button').simulate('click')
+
+      const rect = document.querySelector('.popup.ui').getBoundingClientRect()
+      const { top, left } = rect
+
+      expect(top).to.be.at.least(100)
+      expect(left).to.be.at.least(100)
       assertInBody('.ui.popup.visible')
     })
   })