fix(VFooter,VFab): include padding in measured layout height

packages/vuetify/src/components/VFab/VFab.tsx

@@ -54,7 +54,7 @@ export const VFab = genericComponent()({
     const el = shallowRef<HTMLElement>()
     useResizeObserver(el, entries => {
       if (!entries.length) return
-      height.value = entries[0].contentRect.height
+      height.value = entries[0].target.clientHeight
     })
 
     const hasPosition = toRef(() => props.app || props.absolute)

packages/vuetify/src/components/VFooter/VFooter.tsx

@@ -52,7 +52,7 @@ export const VFooter = genericComponent()({
     const el = shallowRef<HTMLElement>()
     useResizeObserver(el, entries => {
       if (!entries.length) return
-      autoHeight.value = entries[0].contentRect.height
+      autoHeight.value = entries[0].target.clientHeight
     })
     const height = computed(() => props.height === 'auto' ? autoHeight.value : parseInt(props.height, 10))
 

packages/vuetify/src/components/VFooter/__tests__/VFooter.spec.browser.tsx

@@ -0,0 +1,52 @@
+// Components
+import { VFooter } from '..'
+import { VLayout } from '@/components/VLayout'
+import { VMain } from '@/components/VMain'
+
+// Utilities
+import { commands, render, screen } from '@test'
+
+describe('VFooter', () => {
+  it('should reserve layout space equal to its rendered height', async () => {
+    render(() => (
+      <VLayout>
+        <VMain>Content</VMain>
+        <VFooter app>Footer</VFooter>
+      </VLayout>
+    ))
+
+    const footer = screen.getByCSS('.v-footer')
+    const main = screen.getByCSS('.v-main')
+
+    await commands.waitStable('.v-footer')
+
+    // Default $footer-padding is 8px 16px, so the content box is 16px shorter
+    // than the box the footer actually occupies. The layout must reserve the
+    // latter or the last 16px of VMain content renders underneath the footer.
+    const rendered = footer.getBoundingClientRect().height
+    const reserved = parseFloat(getComputedStyle(main).paddingBottom)
+
+    expect(rendered).toBeGreaterThan(0)
+    expect(reserved).toBe(rendered)
+  })
+
+  it('should reserve layout space including custom vertical padding', async () => {
+    render(() => (
+      <VLayout>
+        <VMain>Content</VMain>
+        <VFooter app style="padding-top: 40px; padding-bottom: 40px">Footer</VFooter>
+      </VLayout>
+    ))
+
+    const footer = screen.getByCSS('.v-footer')
+    const main = screen.getByCSS('.v-main')
+
+    await commands.waitStable('.v-footer')
+
+    const rendered = footer.getBoundingClientRect().height
+    const reserved = parseFloat(getComputedStyle(main).paddingBottom)
+
+    expect(rendered).toBeGreaterThan(80)
+    expect(reserved).toBe(rendered)
+  })
+})