docs: add esolid example and examples with icons

Author: mrholek

docs/4.0/components/alert.mdx

@@ -255,7 +255,7 @@ Use `variant="solid"` to change contextual colors to solid.
   <CAlert color="danger" variant="solid">A simple solid danger alert—check it out!</CAlert>
   <CAlert color="warning" variant="solid">A simple solid warning alert—check it out!</CAlert>
   <CAlert color="info" variant="solid">A simple solid info alert—check it out!</CAlert>
-  <CAlert color="light" variant="solid" class="text-high-emphasis">A simple solid light alert—check it out!</CAlert>
+  <CAlert color="light" variant="solid" className="text-high-emphasis">A simple solid light alert—check it out!</CAlert>
   <CAlert color="dark" variant="solid">A simple solid dark alert—check it out!</CAlert>
 </Example>
 
@@ -266,7 +266,7 @@ Use `variant="solid"` to change contextual colors to solid.
 <CAlert color="danger" variant="solid">A simple solid danger alert—check it out!</CAlert>
 <CAlert color="warning" variant="solid">A simple solid warning alert—check it out!</CAlert>
 <CAlert color="info" variant="solid">A simple solid info alert—check it out!</CAlert>
-<CAlert color="light" variant="solid" class="text-high-emphasis">A simple solid light alert—check it out!</CAlert>
+<CAlert color="light" variant="solid" className="text-high-emphasis">A simple solid light alert—check it out!</CAlert>
 <CAlert color="dark" variant="solid">A simple solid dark alert—check it out!</CAlert>
 ```