fix: Color contrast ratio accessibility

Fixed Lighthouse "Background and foreground colors have a sufficient contrast ratio" by changing bg color of header area, linkbutton, and filter border and placeholder text. Lighthouse score 87 -> 89

Useful Resource: https://app.contrast-finder.org/

Author: Mandy-cyber

src/App.css

@@ -1,6 +1,6 @@
 .App {
   /* height: 500px; */
-  background-color: #007EE5;
+  background-color: #1E685B;
   text-align: center;
   display: flex;
   justify-content: center;

src/components/LinkButton/LinkButton.css

@@ -9,7 +9,7 @@
   border-radius: 2px;
   box-shadow: 0 1px 4px rgba(0, 0, 0, 0.2);
 
-  background-color: #2ecc71;
+  background-color: #CC2E88;
   color: #fff;
 
   -webkit-transition: background-color 0.3s;

src/components/Navbar/Navbar.css

@@ -1,5 +1,5 @@
 .topnav {
-    background-color:#007EE5;
+    background-color:#1E685B;
     overflow: hidden;
     text-align: right;
 }

src/components/ProjectList/CardsContainer.jsx

@@ -128,7 +128,9 @@ export default class CardsContainer extends React.Component {
               onChange={this.handleSelectChange}
               options={this.filterOptions}
               multi={true}
-              placeholder='Filter'
+              placeholder={<div className='filter-placeholder-text' style={{color: "#757575"}}>Filter</div>}
+              aria-labelledby='Filter'
+              style={{borderColor: "#DCDCDC"}}
             />
           </div>
         </div>